SB 

U) [a I Issued April ti, 1910. 

^\4\% ^' ^' DEPARTMENT OF AGRICULTURE. 
' ' ^' BUREAU OF CHEMISTRY— BULLETIN No. 131. 

^' ' , H. W. WILEY, Chief of Hurmui. 



LEAD ARSENATE. 

I. Composition of lead arsenates found on the market. 
II. ''Home-made" lead arsenate and the chemicals entering into 

its manufacture. 
III. Action of lead arsenate on foliage. 



J. K. HAYWOOD, 

Chief, Miscellaneous Division, 

AND 

c. c. McDonnell, 

Chief, Insecticide and Fungicide Laboratory, Miscellaneous JHvision. 
IN COOPERATION WITH THE BUREAU OF ENTOMOLOGY. 





WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1910. 



Jtono 



graph, 







Book 



I.sstied April 0, 1910. 

U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF CHEMISTRY - BULLETIN No. 131. 



H. W. WILEY, Chief of Biireiui. 



LEAD ARSENATE. 

I. Composition of lead arsenates found on the market. 
II. "Home-made" lead arsenate and the chemicals entering into 

its manufacture. 
III. Action of lead arsenate on foliage. 



rrei 



<BY 

.V 



jfK^UAYWOOD, 

Chief, Miscellaneous Division, 

AND 

c. c. McDonnell, 

Chief, Insecticide and Fungicide Laboratory, Miscellaneous Division. 
IN COOPERATIOxX WITH THE BUREAU OF ENTOMOLOGY. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE, 

1910. 



% 







LETTER OF TRANSMriTAL. 



U. S. Department of Agriculture, 

Bureau of Chemistry, 
Washington, D. C, October 16, 1909. 
Sir: I have the honor to submit for your approval a report on the 
composition of commercial and "home-made" lead arsenates, 
together with the results of two years' experimental work on the 
action of this insecticide on foliage, especially that of the peach tree. 
The problems and conditions discussed are of vital interest to all 
orchardists and farmers, and I recommend the publication of the 
report as Bulletin 131 of the Bureau of Chemistry. The work was 
performed in the insecticide and fungicide laboratory of the Miscel- 
laneous Division of this Bureau, with the cooperation of the Bureau 
of Entomology. 

Respectfully, H. W. Wiley, 

Chief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 

2 



APR 14191U 



CONTENTS 



Page. 

Introduction 5 

I. Compogition of lead arsenates found on the market 6 

Scope of the investigation 6 

Methods of analysis 7 

Results of analyses 9 

Discussion 11 

II . " Home-made ' ' lead arsenate and the chemicals entering into its manufac- 
ture 12 

Introduction 12 

Methods of analysis 13 

Lead salts 13 

Sodium arsenate 13 

Composition of lead acetate 14 

Results of analyses 14 

Discussion 15 

Composition of lead nitrate 15 

Results of analyses 15 

Discussion 15 

Composition of sodium arsenate 15 

Results of analyses 15 

Discussion 16 

Theoretical composition of lead arsenate 17 

Published formulas 19 

Directions for preparing lead arsenate . . . • 21 

Comparative merits of lead acetate and lead nitrate 22 

Physical properties of lead arsenate 23 

III. Action of lead arsenate on foliage 24 

General discussion 24 

Preparation of the lead arsenate used 26 

Experimental work of 1907 27 

Description of experiments 27 

Record of observations 28 

Weather conditions 29 

Summary for 1907 32 

Experimental work of 1908 33 

Description of experiments 33 

Record of observations 34 

Notes made on June 4 34 

Notes made on June 9 35 

Notes made on July 29 on condition of fruit 35 

Notes made on August 13 on condition of fruit 36 

Weather conditions 37 

Summary for 1908 41 

3 



4 CONTENTS. 

III. Action of lead arsenate on foliage — Continued. Page. 

Summary of results for the two years' experiment 42 

General discussion of problems involved in the investigation 43 

Lead nitrate vs. lead acetate 43 

Susceptibility of peach foliage to injury 44 

Cause of the decomposition of lead arsenate 45 

Experiments on the action of the carbon dioxid of the air 45 

Experiments on the solvent action of water used in spraying. 46 

Conclusions 48 

List of tables 50 



LLUSTRATIONS. 



PLATES. 

Page. 
Plate L Effect of different treatments on the settling of lead arsenate. Fig.l. — 24 
After standing two minutes. Fig. 2. — After standing fifty minutes. 
II. Peach leaves showing injury from lead arsenate. Fig. 1. — Leaves 
from trees in Experiment 3. Fig. 2. — Leaves from trees in Ex- 
periment 12 34 

III. Check plot, not sprayed, showing normal, healthy foliage of peach 

trees 36 

IV. Peach tree in Experiment 12 sprayed with lead arsenate and show- 
ing partial defoliation 36 

TEXT FIGURE. 

Fig. 1. Injured peaches fr(jni trees sprayed with lead arsenate 37 



LEAD ARSENATE. 



INTRODUCTION. 

It is only in more recent years that lead arsenate has been used as 
an insecticide for spraying purposes. Its use was first suggested by 
Mr. F. C. Moulton in 1892, while acting as chemist for the gypsy 
moth commission of Massachusetts, after having made a study of 
numerous materials to be used as insecticides for the extermination 
of the gypsy moth. It was found that Paris green could not be 
used successfully for this purpose, principally because it could not be 
applied in sufficient quantity to kill the caterpillars without seriously 
injuring the foliage. Wliile lead arsenate was not found entirely 
satisfactory in destroying this pest,-it possessed several advantages 
over Paris green, and this has resulted in its replacing the latter 
material for spraying purposes to a very large extent, in fact, almost 
entirely in some of the Rocky Mountain and Pacific Coast States. 
Some of these advantages are: (1) It is not so injurious to foliage 
when applied thereto, on account of its being less soluble in water. 
(2) When sprayed upon leaves it forms a thin film, which is quite 
adhesive and is not so easily washed off by rains. (3) It remains in 
suspension much better, thereby requiring less effort to keep the mix- 
ture agitated, and thus insuring a more uniform application. (4) 
Being white, it forms a visible coating and is easily distinguished 
when it has been applied. 

The initial cost of this material is slightly greater than that of Paris 
green, owing to the fact that it contains a smaller percentage of arsenic 
than the latter, and therefore more of it must be used to produce the 
same effect. Because of its greater adhesive qualities, however, it 
remains on the foliage better, requiring less frequent application, and 
thus in the end lead arsenate is no more expensive than Paris green; 
in fact, it may be even cheaper, as the greatest expense in spraying 
is the cost of applying the material to the trees. 

The use of lead arsenate has increased very rapidly during the last 
few years, as is shown by the fact that less than ten years ago no one 
was manufacturing it to any large extent, while at the present time 
there are at least eighteen manufacturing chemists in the United 
States making it in greater or less quantities, and a number of other 
firms are preparing to do so. An attempt was made to determine the 
total amount sold in the United States for the years 1907 and 1908 by 
writing to the various manufacturers for figures showing their sales. 

6 



6 LEAD ARSENATE, 

Many of these very cheerfully gave the information asked for, but 
several refused, and a few others did not have the data available. 
Judging from the information which has been obtained, the total 
amount sold in 1908 was approximately 2,500 tons, the value of which 
was more than half a million dollars. In addition, a great quantity 
of the home-made material has been used, but this quantity can not 
be estimated. 

It was on account of the great importance which lead arsenate is 
assuming for spraying purposes and in view of certain variable results 
which have been reported, that this study was begun by the Bureau 
of Chemistry two years ago, principally for the purpose of determin- 
ing, if possible, the conditions which cause it to be injurious to foliage 
in some cases. The experiments have been conducted for two suc- 
cessive years, as it was considered impossible to arrive at any trust- 
worthy conclusions in a shorter period. At the same time a study of 
the composition of the lead arsenates found on the market and also 
that of "home-made" lead arsenate was made, including analyses of 
such of the chemicals entering into its manufacture as could be pro- 
cured from druggists and other sources. 

This work, therefore, has been divided into three parts, as follows: 

I. Composition of lead arsenates found on the market. II. ''Home- 
made" lead arsenate, and the chemicals entering into its manufacture. 
III. Action of lead arsenate on foliage. 

The work has been carried out in cooperation with the Bureau of 
Entomology, Mr. A. L. Quaintance, in charge of deciduous-fruit 
insect investigations, having furnished the larger number of the sam- 
ples herein reported and cooperated in the carrying out of the spraying 
experiments outlined in the third section. 

I. COMPOSITION OF LEAD ARSENATES FOUND ON THE MARKET. 
SCOPE OF THE INVESTIGATION. 

The object of this investigation was to determine by chemical 
analysis the quality or grade of the leading lead arsenates as found 
on the open market and supplied to the trade. To this end samples 
were obtained at many points in different sections of the United 
States by various collectors, and, while the products of a few manu- 
facturers are not represented, all of the leading brands, representing 
about 98 per cent of the total output, are included in the list. In a 
number of instances several samples of the same brand, purchased 
at different times and places, have been analyzed in order to deter- 
mine whether the output of the same firm is of uniform composition. 
As the purpose of the investigation was to show the general condition 
of the trade during 1907-8, more particularly as a preliminary to 
other studies, the names of the manufacturers are not given, but all 
of the samples from one firm are designated by the same letter, that 
they may be compared. 



COMPOSITION OF LEAD AKSENATES ON THE MAKKET. 7 

METHODS OF ANALYSIS. 

The samples were analyzed according to the provisional methods 
of the Association of Official Agricultural Chemists", as follows: 

PREPARATION OF SAMPLE. 

In case the sample is in the form of a paste, as it usually is, dry the whole of it to 
constant weight at the temperature of boiling water and calculate the results as total 
moisture. Grind the dry sample (which will gain a small amount of moisture by so 
doing) to a fine powder and determine the various constituents as follows: 

MOISTURE. 

Weigh 2 grams of the sample and heat in a water bath for eight hours or in a hot air 
bath at 110° C. for from five to six hours, or till constant weight is obtained. 

TOTAL LEAD OXID. 

Dissolve 2 grams of the sample in about 80 cc of water and 15 cc of concentrated 
nitric acid on the steam bath; transfer the solution to a 250 cc flask, and make up to 
the mark. To 50 cc of the solution add 3 cc of concentrated sulphuric acid, evapo- 
rate on the steam bath to a sirupy consistency, and then on the hot plate till white 
fumes appear and all nitric acid has been given off. Add 50 cc of water and 100 cc 
of 95 per cent alcohol. Let stand for several hours and filter off supernatant liquid, 
wash about ten times with acidified alcohol (water 100 parts, 95 per cent alcohol 200 
parts, and concentrated sulphuric acid 3 parts), and then with 95 per cent alcohol till 
free of sulphuric acid. Dry, remove as much as possible of the precipitate from the 
paper into a weighed crucible, and ignite at low red heat. Burn the paper in a sepa- 
rate porcelain crucible and treat the residue first with a little nitric acid, which is 
afterwards evaporated off, and then with a drop or two of dilute sulphuric acid. Ignite, 
weigh, and add this weight to the weight of the precipitate previously removed from 
the paper for amount of the lead sulphate. If preferred, the lead sulphate may be 
filtered and weighed in a porcelain Gooch crucible. 

TOTAL ARSENIC OXID (MODIFIED GOOCH AND BROWNING METHOD b). 

Transfer 100 cc of the nitric acid solution of the sample, prepared as in the above 
determination of lead, to a porcelain dish, add 6 cc of concentrated sulphuric acid, 
evaporate to a sirupy consistency on water bath and then on hot plate to the appear- 
ance of white fumes of sulphuric acid. Wash into a 100 cc flask with water, make up 
to mark, filter through dry filter, and use a 50 cc aliquot for further work. Transfer 
this to an Erlenmeyer flask of 400 cc capacity, add 4 cc of concentrated sulphuric 
acid and 1 gram of potassium iodid, dilute to about 100 cc and boil until the volume 
is reduced to about 40 cc. Cool the solution under running water, dilute to about 
300 cc, and exactly use up the iodin set free and still remaining in solution with a few 
drops of approximately tenth-normal sodium thiosulphate. Wash the mixture into 
a large beaker, make alkaline with sodium carbonate and slightly acidify with dilute 
sulphuric acid; then make alkaline again with an excess of sodium bicarbonate. 
Titrate the solution with a twentieth-normal iodin solution to the appearance of a 
blue color, using starch as indicator. 

WATER-SOLUBLE LEAD OXID. 

Place 2 grams of the sample in a flask with 2,000 cc of carbon-dioxid-free water and 
let stand ten days, shaking eight times a day. Filter through a dry filter (being sure 
a clear filtrate is obtained) and use aliquots of this for determining soluble lead and 
arsenic oxids and soluble solids; determine lead as described above for total lead, 

oU. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 239. 
iAmer. J, Sci., 1890, 40: 66. 



8 LEAD ARSENATE. 

using the same relative proportions of sulphuric acid, water, and alcohol, but keeping 
the volume as small as possible. 

WATER-SOLUBLE ARSENIC OXID. 

For this determination use 200 to 400 cc of the water extract obtained under the 
determination of soluble lead oxid. Add 0.5 cc of sulphuric acid and evaporate it to 
a sirupy consistency, then heat on a hot plate to appearance of white fumes. Add a 
very small amount of water and filter off lead through the very smallest filter paper, 
using as little wash water as possible. Place this filtrate in an Erlenmeyer flask, and 
determine arsenic as described under total arsenic oxid, using the same amount of 
reagents and the same dilutions. 

SOLUBLE SOLIDS OR IMPURITIES. 

Evaporate 200 cc of the water extract obtained above to dryness in a weighed 
platinum dish, dry to constant weight at the temperature of the boiling water bath, 
and weigh. The soluble solids so obtained represent principally any sodium acetate 
or sodium nitrate present, with a very small quantity perhaps of lead acetate or nitrate 
and some soluble arsenic, probably in the form of lead arsenate, or sodium arsenate. 

These methods were not followed exactly in all cases, owing to 
peculiarities of some of the samples. Those which were moist and 
in the form of a paste were heated at about 85° C. till dry enough to 
powder, and the loss noted. The analysis was then carried out on 
this dried sample and the results calculated to the material in its 
original condition. The moisture on the dried sample was calculated 
to the original material and added to the loss obtained on the first 
drying for ''total moisture." 

Insoluble matter was that remaining from the treatment with nitric 
acid and was removed by filtration, washed, ignited, and weighed. 

In case calcium is present in the sample, it may be separated from 
the lead by treating the precipitated sulphates with water (acidified 
with sulphuric acid) to which no alcohol has been added and filtering, 
or by the following method, which is the one used in this work: 

Precipitate the lead from a solution slightly acidified with nitric acid, with hydrogen 
sulphid in the cold; filter off the precipitate containing the lead sulphid, wash, 
dissolve in moderately strong hot nitric acid, treat this solution with 4 or 5 cc of 
concentrated sulphuric acid, carry down in a porcelain dish to expel nitric acid, treat 
with water and alcohol mixture, and proceed as before. Calcium is determined in the 
filtrate from the lead sulphid (after removing any arsenic remaining therein by hydro- 
gen sulphid) by precipitating with ammonia and ammonium oxalate in the regular 
way. 

In case the material was lead arsenite or contained this substance, it 
was determined as follows: 

Boil 2 grams of the sample with 50 cc of dilute (1 to 5) sulphuric acid for about 
one hour, cool, make up to mark, filter through dry filter, and to 50 cc of the filtrate 
add sodium bicarbonate in considerable excess and titrate with standard iodin solu- 
tion, using starch as indicator. The arsenic equivalent of the iodin solution used is 
calculated as arsenious oxid (AsjOs). 

Tests were made on the water soluble impurities for acetates and 
nitrates. This would indicate which lead salt had been used in the 
manufacture of the sample. 



COMPOSITION OF LEAD ARSENATES ON THE MARKET. 



RESULTS OF ANALYSES. 

Table I, — Composition of commercial lead arsenates. 
ANALYSIS OF ORIGINAL SAMPLE. 



Serial 


















num- 
ber 
and 


Mois- 


Acid in- 


Total 
lead 


Total 
arsenic 


Water- 
soluble 


Water- 
soluble 
lead 
oxid 
(PbO). 


Water- 
soluble 


Soluble 


letter 


ture. 


soluble 


o.xid 


oxid 


impuri- 


arsenic 
o.xid 

(AS2O5). 


impurities 


indi- 
cating 






(PbO). 


(AsjOs). 


ties. 


contain— 


firm. 


















A: 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


Per cent. 




4535 


61.84 


0.03 


23.06 


12.62 


2.03 


0.15 


0.31 


Nitrates. 


4629 


44.69 


.05 


35.45 


17.97 


.55 


.06 


.38 


Do. 


4656 


59.65 


.04 


25.27 


13.66 


.75 


.09 


.22 


Do. 


5084 


47.91 


.03 


32.50 


17.13 


.80 


.18 


.33 


Do. 


5086 


40.63 


.14 


42.23 


14.49 


1.34 


.75 


.50 


Acetates. 


5087 


52. 02 


.03 


30.06 


15.64 


.05 


.09 


.25 


Nitrates. 


5088 


48.21 


.04 


32.11 


16.99 


.99 


.16 


.33 


Do. 


5089 


45.00 


.02 


35.53 


16.93 


.32 


.29 


.43 


Do. 


5090 


42.75 


.06 


36.07 


17.55 


1.42 


.25 


.37 


Do. 


5853 


.41 


.05 


66.75 


28.91 


.66 


1.06 


1.06 


Acetates. 


5854 


48.05 


.04 


32.75 


16.86 


1.51 


.31 


.32 


Nitrates. 


6451 


41.36 




37.79 


17.38 


.76 


.48 


.82 


Acetates. 


B: 

6456 


42. 61 




39.49 


14.44 


1.06 


.32 


. 41 


Do. 


C: 

a 5341 


44.70 




41.46 


12.16 


.08 


.28 


.11 


Do. 


D: 

4633 


36.89 


.28 


39.75 


17.76 


4.51 


.16 


.50 


Do. 


6 4651 


46.38 


.03 


35.03 


14. 65 


3.71 


.17 


.22 


Do. 


6 4652 


37. 76 


.11 


40.66 


17.23 


3.20 


.18 


.30 


Do. 


5085 


37.61 


.08 


40.92 


17.76 


1.27 


.21 


.36 


Do. 


5091 


31.54 


.06 


48.09 


15.69 


2.18 


.22 


.22 


Do. 


5961 


41.18 


.05 


35.48 


18.81 


4.33 


.55 


.20 


Nitrates. 


6452 


21.41 




46.80 


22.11 


5.68 


.67 


.06 


Do. 


E: 

C4720 
F: 

4291 


45.60 


3.42 


26.97 


12.08 


7.54 


1.19 


2.42 


Acetates. 


40.89 




36.46 


19.60 


1.04 


.37 


.33 




6 4301 
G: 

4533 


48.29 


."o-i' 


33.89 


15.46 


2.23 


.29 


.33 


Do. 


28.39 


.04 


49.67 


20.49 


2.03 


.49 


1.01 


Do. 


5611 


37.89 




43.88 


14.87 


.77 


10 


.13 

1.08 


Do 


5855 


1.89 


.05' 


64.64 


28.06 


3.80 


L04 


Do! 


5856 


45.60 


.03 


37.93 


14. 33 


.64 


.30 


.41 


Do. 


6454 


34.24 




45.64 


16.90 


.75 


.58 


.90 

.51 


Do. 
Do. 


H: 

4534 


.57 


.09 


72.57 


24.01 


1.14 


.47 


6453 


48.34 




36.88 


11.98 


1.04 


.44 


.04 

.23 
.24 


Do. 

Nitrates. 
Acetates. 


I: 

4296 


43.08 




38.81 


15.22 


2.32 


22 


4631 


45.84 


.'63' 


35.25 


16.70 


1.34 


!ll 


4632 


45.12 


.29 


35.82 


16.70 


.44 


.12 


.26 


Do. 


6 4648 


45.20 


.04 


36.58 


16.24 


.68 


.19 


.30 


Do. 


4657 


40.38 


.11 


40.04 


17.83 


.65 


.36 


.32 


Do. 


4721 


.59 


.03 


67.14 


28.87 


2.01 


.21 


.44 


Do. 


4830 


46.34 


.07 


34.44 


16.56 


.93 


.13 


.26 


Do. 


5852 


.67 


.67 


65.24 


26.42 


1.39 


.60 


.58 


Nitrates. 


5959 


47. 56 


.03 


35.06 


15.98 


.74 


.35 


.39 


Do. 


4657 


41.03 




38.46 


16.24 


1.45 


.44 
.44 


.71 
5.45 


Do. 
Acetates. 


J: 

d4644 
K: 


2.00 


.05 


51.35 


43.81 


2.27 


6455 


35.75 




44.64 


16.43 


.67 


.40 
.63 


.87 
2.12 


Do. 
Do. 


L: 

e4532 


35. 43 


.06 


44.73 


18.04 


.88 


/6458 
M: 

4624 

N: 


41.40 
.76 




45.62 
60.06 


6.03 
28.52 


3.35 
5.40 


1.61 
.38 


.02 
.30 




.11 


Nitrates. 


4571 


61.03 


.23 


23.31 


12.89 


2.03 


.19 


.21 


Do. 


4630 
O: 


22.18 


.09 


50.55 


25.15 


.83 


.29 


.80 


Acetates. 


4870 


38.81 


.21 


37.98 


20.91 


.45 


.15 


.45 


Nitrates. 


5960 


43.26 


.03 


36.02 


19.36 


.40 


.42 


.53 


Do. 



a Sample had distinct odor of ammonia; on determination gave 0.14 per cent on original sample. 

bample had decided acid reaction; strong odor of acetic acid. 
^ ''i'"?!;^'"'''^ ^•'*^ P^'" ^'^^^ 0' <^'*0. l-^S per cent of CO2; calculated to moisture-free basis, 4.56 per cent of 
CaO, 3.22 percent of CO2. ' 

d Mostly lead arsenite. Total arsenic reported as AS2O3, 43.81 per cent; of this, 3.37 per cent (03.91 
per cent AsjOs) is present as arsenate; soluble arsenic reported as AS2O3. 

e Sample labeled " lead arsenite; " a mixture of lead arsenite and lead arsenate. Arsenic as arsenite 6.52 
per c^nt of AS2O3 (07.57 per cent of AsjOs); as arsenate 10.47 per cent of AS2O5. Calculated to moisture- 
free basis AsiOa^ 10.01 per cent; As206= 16.31 per cent. Water-soluble arsenic reported as AS2O3. 

/ Contains an excess of lead as carbonate. 

23904— Bull. 131—10 2 



10 



LEAD ARSENATE. 



Table I. — Composition of commercial lead arsenates — Continued. 
CALCULATED TO MOISTURE-FREE BASIS. 



Serial 












1 


num- 
ber 
and 
letter 
indi- 
cating 


Acid 
insoluble. 


Total 

lead oxid 

(PbO). 


Total 
arsenic 

oxid 
(AsjOs). 


Water- 
soluble 
impurities. 


Water- 
soluble 
lead oxid 
(PbO). 


Water- 
soluble 
arsenic 

oxid 
(AS2O6). 


firm. 














A: 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


Per cent. 


4535 


0.08 


60.43 


33.07 


5.32 


0.39 


0.81 


4629 


.09 


64.09 


.32. 49 


.99 


.11 


.69 


4656 


.10 


62. 63 


33.85 


1.86 


.22 


.55 


5084 


.06 


62.39 


32.89 


1.54 


.35 


.63 


5080 


.24 


71.13 


24.41 


2.26 


1.26 


.84 


5087 


.07 


62.65 


32.60 


1.35 


.19 


.52 


5088 


.08 


62.00 


32.81 


1.91 


.31 


.64 


5089 


.03 


65.31 


31.12 


.59 


.53 


.79 


5090 


.11 


63.00 


30.66 


2.48 


44 


.65 


585.3 


.05 


67.03 


29.03 


.67 


1.06 


1.06 


5854 


.08 


63.04 


32.45 


2.91 


.60 


.60 


6451 
B: 

6450 
C: 

5341 
D: 




64.44 
68.80 
74.97 


29.64 
25.16 
21.99 


1.30 

1.85 

.14 


.82 
.56 
.51 


1.40 
.71 
.20 








4033 


.44 


62.99 


28.14 


7.15 


.25 


.79 


4651 


.06 


65.33 


27.32 


6.91 


.32 


.41 


4652 


.18 


05.33 


27.68 


5.14 


.29 


.48 


5085 


.13 


65.59 


28.47 


2.04 


.34 


.58 


5091 


.09 


70.25 


22.92 


3.18 


..32 


.32 


5961 


.09 


60. 32 


31.98 


7.36 


.94 


.34 


0452 
E: 

4720 
F: 
4291 
4301 
G: 




59.54 
49.58 


28.13 
22.21 


7. 22 
13.86 


.85 
2.19 


.08 
4.45 


6.29 




61. 68 
65.54 


33.16 
29.90 


1.76 
4.31 


.63 
.56 


.56 
.64 






4533 


.06 


69.36 


28.61 


2.83 


.08 


1.41 


5611 
5855 




70.65 
65.78 


23.94 
28.60 


1.24 
3.87 


.16 
1.06 


.21 
1.10 


.65" 


5856 


.06 


69.72 


26.34 


1.18 


.55 


.77 


6454 
H: 




69.40 


25.69 


1.14 


.88 


1.37 




4534 


.09 


72.99 


24.15 


1.15 


.47 


.51 


6453 
I: 

4296 
4631 




71.39 

68.18 
65.08 


23.19 

26.74 
30.95 


2.01 

4.08 

2.47 


.85 

.40 
.20 


.08 

.40 
.44 




'.m" 


4632 


.53 


65.27 


30.43 


.80 


22 


.47 


4648 


.07 


66.75 


29.64 


1.24 


.35 


.55 


4657 


.18 


67.16 


29.91 


1.09 


.60 


.54 


4721 


.03 


67.54 


29.04 


2.02 


.21 


.44 


4830 


.13 


64.18 


30.86 


1.73 


.24 


.48 


5852 


.67 


65.68 


26.60 


1.40 


.60 


.58 


5959 


.06 


66.86 


30.47 


1.41 


.67 


.74 


4657 

J: 
4644 

K: 
6455 

L: 
4532 




65.20 
52.40 


27.54 
44.70 


2.47 
2.32 


.75 
.45 


1.20 
5.56 


.05 




69.48 
69.27 


25.57 
27.94 


1.04 
1.36 


.62 
.98 


1.35 
3.28 


.09 


6458 
M: 




77.93 


10.30 


5.72 


2.75 


.03 




4624 
N: 

4571 


.11 


60.52 


28.74 


5.44 


.38 


.30 


.59 


59.82 


33.08 


5.21 


.50 


.54 


4630 


.12 


04.96 


i 32. 32 


1.07 


.37 


1.03 


O: 














4870 


.34 


62.07 


[ 34. 17 


.74 


.24 


.74 


5960 


.05 


63.48 


! 34. 12 


.70 


.74 


.93 



COMPOSITION OF LEAD ARSENATES ON THE MARKET. 11 

DISCUSSION. 

Some of the samples examined had dried out considerably before 
thev were received, as was evident from their mechanical condition, 
weight of package, etc. In such cases the per cents given on the origi- 
nal sample are based on the goods as received and will not represent 
the correct composition of the material as placed on the market, on 
account of this decrease in the moisture content, making the per cent 
of the other constituents as given higher than they were originally. 

In making lead arsenate from lead acetate and disodium arsenate 
a certain amount of acetic acid is formed. This hatl not been com- 
pletely washed out in all cases, as was shown by the fact that several 
of the samples had a strong odor of acetic acid. No quantitative 
determination was made of the amount, but as it would be driven 
off at the temperature of drying, the term "moisture" not only 
includes water, but any other material volatile at from 105° to 1 10° C. 

One of the samples examined was lead arsenite and another was 
a mixture of the arsenate and arsenite in about equal proportions. 
Several others contained small amounts of arsenic as arsenite, but 
usually only traces were present. In such cases the water-soluble 
arsenic reported as arsenic oxid (AsgOj) contained some arsenious 
oxid. As soluble arsenic is injurious in either form, the two have 
not been determined separately, except in the cases noted, where it 
was present entirely as arsenite. 

On inspecting the analyses given in Table I, the first striking fact 
that will be observed is the great variation in the composition of the 
different samples. The content of arsenic oxid ranges from 6.03 to 
43.81 per cent (the latter as AsjOg); lead oxid varies from 23.06 to 
72.57 per cent; moisture from 0.41 to 61.84 per cent; water-soluble 
arsenic from 0.02 to 5.45 per cent (AsjOg) ; and water-soluble impur- 
ities from 0.08 to 7.54 per cent. 

In order to secure a more uniform basis for comparison all of the 
determinations have been calculated to moisture-free material. A 
much greater uniformity is shown when this is done, but there is 
still a considerable variation. Arsenic oxid ranges from 10.30 to 
44.70 per cent (the latter As^Og); lead oxid from 49.58 to 77.93 per 
cent; water-soluble arsenic oxid from 0.03 to 5.56 per cent (AsjOg); 
and water-soluble impurities from 0.14 to 13.86 per cent. 

Evidently in some cases the salts formed as by-products in the 
manufacture have not been washed out, or at most the material 
has simply been run through the filter press to remove the super- 
fluous liquid, as is shown by the high per cent of water-soluble mate- 
rial in a number of samples. 

Lead arsenate is recommended for spraying purposes mixed with 
water in various proportions. A standard formula and one fre- 
quently recommended is 2 pounds to 50 gallons. It is easy to see 



12 LEAD ARSENATE. 

from the analyses of these samples that if they were made up accord- 
ing to this formula there would be in some cases eight times as much 
arsenic applied as in others. As a consequence the spraying might 
be condemned as inefficient in certain cases, owing to too weak an 
application, while in others, using the very same formula, severe 
injury to the tree might result from too strong an application. An- 
other and even more serious condition may result from a high per 
cent of soluble arsenic, due to the lead arsenate being carelessly or 
improperly made. Where sufficient care is exercised in the making 
the soluble arsenic should certainly not exceed 0.75 of 1 per cent, 
calculated as arsenic oxid (AsgOj) on a 50 per cent moisture basis, or 
1.5 per cent on a moisture-free basis. 

Lead arsenate should be packed in air-tight packages, in order to 
keep it in a moist condition until ready for use. After it has once 
been dried it is much more difficult to keep it in suspension during 
spraying, which often results in an unequal application. This is 
the main reason for putting it up in a moist condition instead of in 
the dry state. Forty to fifty per cent of moisture is sufficient to 
preserve it in good condition, if it is kept in air-tight receptacles 
until used. In case a package is opened and only partly used, that 
remaining may be held over in good condition for the next spraying, 
by covering it with an inch or more of water. Lead arsenate should 
always be bought in original packages, which are plainly labeled; 
when purchased from a broken package, more or less risk is run of 
not getting true lead arsenate. Three instances have been found in 
which supposed "lead arsenate" was purchased from drug stores, 
which on anal3^sis proved to be white arsenic (arsenious oxid). The 
result of spraying this material on the peach or any other fruit tree 
would be disastrous. 

While some of the firms are making a good product, this can not be 
said of all. It was not to be expected, however, that a perfect product 
would be produced in all cases, especially as the material has not 
been manufactured until recently and evidently some have taken 
up the business without proper knowledge of the subject. The 
product will no doubt be improved as its use and preparation become 
better understood. 

II. " HOME-MADE " LEAD ARSENATE AND THE CHEMICALS 

ENTERING INTO ITS MANUFACTURE. 

INTRODUCTION. 

As has been previously noted, arsenate of lead was first proposed 
as an insecticide in 1892, but it was several years before it was used 
to any great extent. This was not a product that could be obtained 
on the market at that time and it was therefore necessary for those 
using it to prepare their own supply. These conditions no longer 



HOME-MADE LEAD ARSENATE. 13 

exist, as there are at the present time twenty or more firms in different 
parts of the United States which manufacture it, and it is possible 
to procure it in almost any section of the country. Only those 
brands should be accepted, however, which bear the guaranty of a 
reliable manufacturer on the package. When such can not be 
obtained at a reasonable price, or if only a small amount is needed, 
it may be advantageously made at home by following the directions 
which are given herein. Again, in some cases where a large quantity 
is to be used and the proper chemicals can be purchased at a reason- 
able })rice, a considerable saving might result by making it at home, 
but this would probabl}^ not be advisable as a general rule. In the 
making of such a product there is alw^ays some risk due to poor chem- 
icals, an incorrect formula, or carelessness in making. The chemicals 
used in its preparation are sotlium arsenate and either lead acetate 
or lead nitrate. All of these can be easily obtained from druggists 
and are the cheapest compounds containing the necessary elements 
in a suitable form. The wholesale prices of the technical gratles of 
these chemicals at the present time are: Lead acetate, 7f to 8 cents 
per pound; lead nitrate, 7f to 8j cents per pound; sodium arsenate, 
5^ to 6 cents per pound. These salts all show some variation in their 
composition and at times this may be very great, particularly in the 
case of sodium arsenate, which is the salt used to supply the arsenic. 
Samples of these chemicals have been obtained in various parts of the 
country from tlruggists and other sources and subjected to analysis. 
In the lead salts the total amount of lead oxid has been determined 
and in the sotlium arsenate total arsenic oxid and chlorin. These are 
the only substances which it is necessary to consider, as they are the 
ones that enter into the reaction. 

METHODS OF ANALYSIS. 
LEAD SALTS. 

Total lead oxid. — This may be determined as sulphate by precipi- 
tating w^ith sulphuric acid, or as oxid by precipitating with ammonia 
and ammonium carbonate and converting into the oxid by ignition. 
The details of these methods are given in works on quantitative anal- 
ysis and both give satisfactory results. 

SODIUM ARSENATE. 

Total arsenic oxid. — Dissolve 2 grams of the sample in water and 
make volume up to 250 cc. Heat 50 cc of this solution to about 
80° C, add 3 grams of potassium iodid and 50 cc of concentrated hy- 
drochloric acid. Let stand fifteen minutes, cool, add approximately 
tenth-normal sodium thiosulphate solution just to disappearance of 
color caused by free iodin. (The end point is easy to obtain without 
the use of starch.) Add immediately sodium carbonate until most 
of the acid is neutralized, then after all the sodium carbonate has 



14 



LEAD ARSENATE. 



been dissolved complete the neutralization with sodium bicarbonate, 
adding it in considerable excess. Add a few drops of starch indicator 
(made by boiling 1 gram of pure starch in 100 cc of water) and run in 
standard iodin solution till all arsenite has been oxidized to arsenate 
as will be shown by the appearance of the blue color. Calculate the 
amount of arsenic present in terms of arsenic oxid (AsjOg) from the 
volume of the standard iodin solution required for the oxidation. 

The strength of the standard iodin solution is determined by 
titrating against a solution containing a known amount of arsenious 
oxid, in the same manner. 

Chlorin {Volhard's method). — Acidify with nitric acid 50 cc of the 
solution used for determining total arsenic, then add an excess of 
standard silver nitrate solution and make up to 200 cc. Filter through 
a dry filter and determine the excess of silver in 100 cc of the filtrate 
by titrating with standard ammonium sulphocyanate solution, using 
solution of ferric alum as indicator. Twice the amount of silver in 
this 100 cc portion, subtracted from the total amount added, will give 
the amount of silver equivalent to the chlorin in the 50 cc of the solu- 
tion originally taken, from which the per cent of chlorin uresent may 
be calculated. 

COMPOSITION OF LEAD ACETATE. 



RESULTS OF ANALYSES. 

In Table II are given the analyses of the samples of lead acetate 
examined. In column four is given the equivalent of the lead oxid 
found in crystallized lead acetate, Pb(C2ll302)2'3H20, in order to show 
more clearly the relative value of the various samples for the purpose 
of making lead arsenate. 

Table II. — Composition of lead acetates. 



Serial 
number. 



4546 
4650 
4626 
4719 
4718 
4538 
4544 
4545 
4627 
4655 
4539 
4540 
4645 
4647 
4543 
4537 
4642 
4832 



Grade. 



White 

White 

Commercial 

White 

Brown 

Pure granulated 

Pure granulated 

Pure granulated 

Purified granulated. 

Commercial 

Purified granulated. 
Purified granulated. 

Purified 

C. P. powdered 

C. P. crystallized... 

Purified 

Commercial 

Commercial 



Lead 

oxid 

(PbO). 



Lead oxid 
calculated 

to 

crystallized 

lead 

acetate. o 



58.84 
59.29 
66.43 
59.93 
60.94 
59.97 
60.76 
60.67 
66.77 
59.00 
58.76 
60.76 
60.34 
65.24 
58.83 
59.37 
63.59 
61.43 



Per cent. 
100.11 
100.88 
113.03 
101.97 
103. 69 
102. 04 
103. 38 
103. 23 
113.61 
100. 39 
99.98 
103. 38 
102. 67 
111.00 
100.10 
101.02 
108. 20 
104. 52 



a Formula, Pb(C2H302)8 SHjO. 



HOME-MADE LEAD ARSENATE. 



15 



DISCUSSION. 

Pure crystallized lead acetate contains theoretically 58.81 per cent 
of lead oxid and 14.25 per cent of water of crystallization. A number 
of these samples have lost much of their water of crystallization, as is 
shown by the high lead content. The commercial "brown" acetate 
of lead is cheaper than the pure crystallized salt and the samples 
examined contained more lead. Voi these reasons the technical 
grade is to be preferred rather than the pure salt for the preparation 
of lead arsenate. None of the samples examined contained impuri- 
ties which would in any way decrease their value for this purpose. 
One hundred pounds of samples Nos. 4626 and 4627 would be equiva- 
lent to over 113 pounds of the crystallized salt for this purpose, in 
addition to being cheaper per pound. 

COMPOSITION OF LEAD NITRATE. 
RESULTS OF ANALYSES. 

The results for total lead oxid in the samples of lead nitrate analyzed 
are as follows : 

Ta b l e III. — Composit ion of lead nitrates . 







Calculated 


Serial 


Lead oxid 


to lead 


number. 


(PbO). 


nitrate 







[Pb(N03)2]. 


Per cent. 


Per cent. 


a 4541 


67.09 


99.60 


a 4550 


07.03 


99.51 


b 4628 


66.33 


98.48 


b 4654 


66. 19 


98.27 


a 4646 


67.10 


99.62 



'C. P." 
'Commercial. 



DISCUSSION. 



The theoretical per cent of lead oxid in pure lead nitrate is 67.35. 
It will be seen that all of these samples contain very close to this 
amount. The composition of lead nitrate is more uniform than lead 
acetate, and it also contains more lead, though some of the partially 
dehydrated samples of the acetate contain nearly as much. 

• COMPOSITION OF SODIUM ARSENATE. 

RESULTS OF ANALYSES. 

Pure crystallized sodium arsenate, or, chemically, disodium hydro- 
gen arsenate, has the formula Na2nAs047H20, and contains theo- 
retically 36.84 per cent of arsenic oxid (AsoOg). One authority states 
that this salt has the composition Na2HAs04l2H20, and gives direc- 



16 



LEAD ARSENATE. 



tions for making lead arsenate based on this formula. This is mislead- 
ing, as such a salt forms below 18° C." (above this temperature it loses 
water rapidly) and it is not the ordinary sodium arsenate of commerce. 
The pure crystallized salt, however, is too expensive for the purpose 
in question and it is necessary to employ the technical grades. These 
are very cheap and if we can be assured of the absence of objectionable 
impurities they are just as good as the pure salt for making lead 
arsenate. In fact they usually contain more arsenic oxid than the 
crystallized salt, owing to the fact that they have been fused and do 
not contain water of crystallization, which theoretically amounts to 
40.4 per cent in the pure salt. Frequently, however, they contain 
large amounts of impurities, usually sodium chlorid, which lowers the 
per cent of arsenic oxid. Sodium arsenate sold for technical purposes 
comes in varying degrees of purity, concerning which there has been 
much confusion. Two grades commonly on the market are the 50 
per cent and the 65 per cent grades, which figures refer to the arsenic 
oxid (AS2O5) content. In only one sample examined was the arsenic 
oxid over 45 per cent. 

In Table IV is given the total arsenic oxid and chlorin in the sam- 
ples of sodium arsenate examined. 

Table IV. — Composition of sodium arsenates. 



Serial 


Arsenic 
oxid 

(AS2O5). 


Chlorin 


number. 


(01). 




Per cent. 


Per cent. 


4547 


44.65 


0.43 


4649 


68.07 


.39 


4625 


44.59 


12.58 


4717 


42.74 


15.17 


4548 


37.39 


.00 


4623 


37.23 


.00 


4831 


37.08 


.00 


4549 


37.29 


.00 


4653 


39.33 


17.72 


4643 


.37. 51 


15.28 


4542 


37.11 


.11 



DISCUSSION. 

All of the samples were tested for arsenic present as arsenite, 
but none was found except traces in two or three of the commercial 
samples. Nos. 4542, 4548, 4549, 4623, and 4831 are samples of the 
pure crystallized salt, and all of them have effloresced to a slight 
extent, which accounts for the arsenic content being a little above 
the theoretical amount. No. 4547 is comparatively pure and con- 
tains nearly 8 per cent more arsenic oxid than the crystallized salt, 
owing to partial dehydration. Nos. 4625, 4643, 4653, and 4717 
are technical samples and are very impure, containing large amounts 

"Fresenius, J. prakt. Chem., 1852, .56:30. 



HOME-MADE LEAD ARSENATE. 17 

of sodiiiiu chlorid, as shown by the high chloiin content. On account 
of this, none of them is desirable for making lead arsenate. Sample 
No. 4649 is a technical sample and is unusually high in arsenic oxid. 
It is probably composed largely of sodium dihydrogen arsenate 
(NaU^AsO,). " 

The analyses here reported show that there is little or no risk in 
buying the technical grades of the lead salts, but sodium arsenate 
is much more variable, and when chlorin is present sufficient lead 
inust be added to combine with this as well as with the arsenic. 
This is a waste of the lead salt, as lead chlorid is not considered of 
value as an insecticide and therefore the presence of chlorids is 
objectionable, particularly in amounts greater than 3 or 4 per cent. 
The presence of arsenious oxid (AsjOg) or sodium arsenite is also 
objectionable, as by uniting with lead it forms lead arsenite, which 
is more soluble than the arsenate, does not remain in suspension 
as well, and, as shown by Kirkland and Burgess, '^ is less poisonous 
to insects. 

THEORETICAL COMPOSITION OF LEAD ARSENATE. 

As has been pointed out by others, arsenate of lead may mean 
any of the various lead arsenates, but the most common ones are 
the tri-plumbic arsenate and the plumbic hydrogen arsenate, rep- 
resented by the formulas Pb3(As04)2 and PbllAsO^, respectively. 
Most of the commercial samples consist of a mixture of these two, 
the one predominating depending upon the method used in its 
manufacture. As has been shown by Smith ^ and Haywood,<= 
when lead acetate and di-sodium arsenate are used for its preparation 
the following reaction takes place: 

3Pb(C',H302)23H,0 + L^Xa^HAsOJILO = Pb3(AsO,)3 + 
4NaC^3H3b,3H,0 + 2HC3H3O, + 1 1H,0. 

Using nitrate of lead and di-sodium arsenate, Smith "^ gives the 
reaction thus: 

5Pb(N03)2 + 4Na3HAsO,(H20)" = PbgCAsO,)^ + 2PbHAsO, + 
8NaN03 + 2HNO3 + n (PI^O) . 

Haywood ^ found the reaction to be mainly as follows : 

Pb (N03)2 + Na^HAsO.VH^O = PbHAsO, + 2NaN03 + TH^O. 

« Agriculture of Massachusetts, 1897, p. 379. 
'> Agriculture of Massachusetts, 1897, p. 364. 
f U. S. Dept. Agr., Bureau of Chemistry Bui. 105, p. 1G5. 
rfLoc. cit., p. 365. 
«Loc. cit., p. 166. 
23904— Bull. 131—10 3 



18 LEAD AESENATE. 

In numerous trials with pure salts it was found that the latter 
reaction occurs almost theoretically, though a small amount of the 
tri-plumbic arsenate is usually formed. 

With lead acetate, however, there are other conditions which 
affect the .reaction, probably temperature, concentration, method 
of mixing, etc. In several cases when pure chemicals were used 
the resulting product was found to be principally the plumbic hydro- 
gen arsenate. Most of the samples examined in which the acetate 
was used in the preparation consisted mainly of the tri-plumbic 
arsenate, Pb3(AsOj2- This contains theoretically 74.40 per cent 
of lead oxid (PbO), and 25.60 per cent of arsenic oxid (AS2O5). 

As may be calculated from the reaction previously given, it will 
be found that by using pure crystallized lead acetate (58.81 per cent 
PbO) and crystallized sodium arsenate (36.84 per cent AS2O5) there 
will be required to make 1 pound of tri-plumbic arsenate 1.296 
pounds of lead acetate and 0.695 pound of sodium arsenate, or 
64.55 per cent of lead acetate and 35.45 per cent of sodium arsenate. 

Plumbic hydrogen arsenate, PbllAsO^, contains theoretically 
64.26 per cent of lead oxid (PbO); 33.15 per cent of arsenic oxid 
(AS2O5), and 2.59 per cent of water of constitution. 

Calculating the amount of lead nitrate (67.35 per cent PbO), and 
sodium arsenate (36.84 per cent AS2O5) required to make 1 pound 
of this compound from the second reaction given, the following result 
is obtained: 0.954 pound of lead nitrate, and 0.900 pound of 
sodium arsenate, or 51.43 per cent of lead nitrate, and, 48.57 per cent 
of sodium arsenate. 

However, formulas can not be given based on technical or even 
on pure salts, for a number of reasons: 

(1) Pure salts are too expensive to use. 

(2) The technical grades show considerable variation in composition, as has been 
shown . 

(3) Allowance must be made for other salt-forming compounds in the sodium 
arsenate, notably chlorids, which use up some of the lead salt. 

(4) The lead salt should be in slight excess to insure rendering all of the arsenic 
insoluble. 

(5) Under the varying conditions which exist at the time of making, the reactions 
do not proceed as indicated by theory. 

In regard to the last reason, it may be said that even if the exact 
chemical composition of the salts were known and the correct propor- 
tions calculated tp satisfy the reaction were mixed together, it would 
seldom, if ever, result in a complete combination of the lead and 
arsenic radicals. The only way to proceed, therefore, is either to 
add lead salt considerably in excess of the theoretical amount, or to 
add the lead salt gradually and test from time to time to see when 
it is in excess. The latter method is much the better one. In a few 
of the published formulas attention is called to the necessity of having 



HOME-MADE LEAD ARSENATE. 19 

the lead salt in excess, but in most of them no reference is made to 
this point. In the majority of the formulas, however, the amount 
called for is considerably in excess of the theoretical. This, of course, 
results in a waste of the lead salt, except in rare instances, where 
sodium arsenate containing an unusually high per cent of arsenic is 
being used. In such a case there might not be sufficient lead to 
combine with all of the arsenic, thus leaving the soluble arsenic salt 
in excess and yielding a product that would cause injury to most 
foliage to which it might be applied. 

PUBLISHED FORMULAS. 

A number of formulas for making lead arsenate have been pub- 
lished in the various experiment station bulletins, governmental 
reports, and works on economic entomology. These, as a rule, call 
for lead acetate as the lead salt and show considerable variation in 
the relative proportion of the lead and arsenic salts. The various 
proportions which have been recommended are given below, with the 
number of publications in which they have appeared placed in paren- 
theses. The original proportion given by Moulton '^ and which was 
followed for the preparation of the arsenate of lead used by the Mas- 
sachusetts gypsy moth commission, was sodium arsenate 29.93 per 
cent and lead acetate 70.07 per cent, or sodium arsenate 3 ounces and 
lead acetate 7 ounces. This formula has been repeated in thirteen 
publications. Another proportion, recommended by Fernald ** and 
found by the authors to have been more frequently recommended 
than any other (26 cases) is arsenate of soda 4 ounces and acetate of 
lead 11 ounces. 

The following formulas have also been found : 

Arsenate of soda. Acetate of lead. 

Oz. Oz. 

4 10 (1) 

4 12 (1) 

2i 7H1) 

6 18 (1) 

8 : 24 (3) 

10 25 (1) 

10 24 (5) 

Formulas using arsenate of soda and nitrate of lead have been given 
as follows: 

Arsenate of soda. Nitrate of lead. 

Oz- Oz. 

5 10 (4) 

12 18f (1) 

10 24 (3) 

a Agriculture of Massachusetts, 1893, p. 282. 
6 Maspachusetts Hatch Exper. Sta., Bui. 24. 



20 LEAD ARSENATE. 

The amount of water recommended to be added to these quantities 
varies from 16 to 200 gallons. In some cases one is directed to mix 
the chemicals, then add the water; in other cases to dissolve the chem- 
icals in separate portions of water and then mix the solutions. But in 
only a few cases is attention called to the necessity of having the lead 
salt in excess or a method given for determining when it is in excess. 
The grade of arsenate of soda to be used is sometimes given, but 
usually no reference is made to it. The 4 to 11 formula is based on 
arsenate of soda of 50 per cent strength and the 3 to 7 formula on 
arsenate of soda of 65 per cent strength; that is, 50 per cent and 65 
per cent of arsenic oxid (AsjOj) . 

Some confusion seems to have arisen in regard to arsenate of soda 
and arsenite of soda, as some of the formulas call for the latter, 
though the other salt is no doubt intended. Arsenite of soda is not 
suitable for the purpose. In a few instances the objection to the 
presence of chlorids in the sodium arsenate is referred to, but usually 
this is not mentioned. 

It was the practice originally to add glucose or thick molasses at 
the rate of 2 quarts to 100 gallons for the purpose of increasing the 
adhesive qualities of the mixture. This practice has since been dis- 
continued, as it was found that these substances did not increase 
adhesion, nor was the material eaten any more readily when they 
were present. 

According to some of the published formulas there would be present 
in the prepared mixture less than one-half pound of actual arsenate 
of lead to 150 gallons of water. It is very doubtful whether the appli- 
cation of such a small amount would be of sufficient benefit to pay 
for the trouble of applying it. 

In all of the formulas the lead salt is present in large enough pro- 
portions, under ordinary conditions, to combine with all of the arsenic 
and still be in excess. In extreme cases, however, when sodium 
arsenate was used which contained an unusually large per cent of 
arsenic or of sodium chlorid this would not be true. It is necessary 
that a different formula should be used for different grades of chem- 
icals, and unless the person making the lead arsenate knows the grade 
of material he is working with he will be in the dark as to which for- 
mula to employ. This shows how necessary it is to apply some test 
to determine when sufficient lead has been added, instead of using 
definite amounts of the two salts. The following tests for this purpose 
have been given : 

After mixing the salts, filter a portion and to the clear filtrate add a 
few drops of dilute sulphuric acid, when, if lead is in excess, a white 
precipitate of lead sulphate will be formed. Instead of sulphuric 
acid, there may be added to the clear filtered liquid a few drops of 
chromate or dichromate of potash, when, if lead is in excess, a yellow 



HOME-MADE LEAD ARSENATE. 21 

precipitate of lead chromate will he formed. If to a illtered portion 
of the solution a little of the lead acetate or lead nitrate solution is 
added and a white precipitate produced, it shows that the arsenic 
salt is still in excess and more lead should be added. The objection 
to all of these tests is that the liquid must either be filtered or allowed 
to settle before the test can be applied, either of which takes consid- 
erable time and extra utensils for the purpose. The test described 
in the following directions for making lead arsenate has proven reli- 
able and can be made instantaneously. 

DIRECTIONS FOR PREPARING LEAD ARSENATE. 

This method will give a good product, without any material waste 
of chemicals, and will require a minimum amount of time. For 
every pound of lead arsenate it is desired to make, use — 

Formula A : Ounces. 

Sodium arsenate (65 per cent) 8 

Lead acetate (sugar of lead) 22 

Formula 15: 

Sodium arsenate (05 per cent) 8 

Lead nitrate 18 

If the sodium arsenate employed is 50 per cent strength, use 10^ 
ounces instoatl of 8. Of the pure crystallized salt, 14 ounces would be 
required to furnish the same amount of arsenic oxid as would be fur- 
nished by the given amounts of the 50 and 65 per cent grades if they 
actually contained these per cents. In only one technical sample 
examined, however, was the arsenic oxid content over 45 per cent. 
The formulas are based on lead acetate containing 60 per cent of lead 
oxid and .lead nitrate containing 66 per cent of lead oxid. 

Dissolve each salt separately in from 1 to 2 gallons of water " (they 
dissolve more readily in hot water), using wooden vessels. After 
solution has taken place, pour slowly about three-fourths of the lead 
acetate or nitrate into the sodium arsenate. Mix thoroughly and 
test the mixture by dipping into it a strip of potassium iodid test 
paper,'' wliich will turn a bright yellow if lead is in excess. If the paper 
does not turn yellow, add more of the lead salt slowly, stirring con- 
stantly, and test from time to time. Wlien the solution turns the 
paper yellow sufficient lead salt is present, but if it should occur that 
the papei- does not turn yellow after all the lead salt has been added 
dissolve a little more and add until an excess is indicated. The 

o The solution of lead acetate may have a milky appearance. This will be no objec- 
tion, and it need not be filtered. 

b If potassium iodid test paper can not be obtained it may be prepared by dissolving 
a few crystals of potassium iodid in about a tablespoonful of water and satm-ating 
filter paper or blotting paper with this solution. After the paper has dried, cut into 
strips and keep dry until needed. 



22 LEAD AKSENATE. 

great advantage of this test is that it is not necessary to fiher the 
solution or wait for it to settle. 

If the paper is not at hand, the test may be made by adding a few 
drops of a solution of potassium iodid, when, if lead is in excess, the 
instant the drops touch the solution a bright yellow compound, lead 
iodid, will be formed. 

It is very essential that the lead salt be added in sliglit excess, but a 
large excess should be avoided. 

If the material has been carefully prepared with a good grade of 
chemicals it will not be necessary to filter and wash the lead arsenate 
formed, though it would be a safe precaution to allow the lead arsenate 
to settle, then decant the clear solution and discard it. Approximately 
1 pound of actual lead arsenate will be obtained by using the amounts 
of chemicals specified, which is equivalent to practically 2 pounds of 
commercial lead arsenate in the paste form. It may be made up to 
50 gallons with water if a formula is being used which calls for 2 
pounds of commercial lead arsenate to 50 gallons, or if a stronger 
application is desired add less water. 

As these chemicals are all extremely poisonous, vessels in which 
they have been dissolved or mixed should be plainly marked and 
not used for any other purpose. 

COMPARATIVE MERITS OF LEAD ACETATE AND LEAD NITRATE. 

As far as expense is concerned it makes little difference which of 
these lead salts is used, as their price per pound is practically the same. 
The nitrate may be slightly cheaper, as it contains a higher per cent 
of lead, though some of the commercial samples of lead acetate which 
are nearly free from moisture contain almost as much. A little less 
lead nitrate is required to make the same quantity of lead arsenate, 
since when made from this salt more of the lead hydrogen arsenate is 
formed, which contains a larger per cent of arsenic — on an average 
about 4 per cent more. This compound has also more desirable phys- 
ical properties, as it remains in suspension better. Kirkland " has 
shown that the lead hydrogen arsenate is slightly more poisonous 
than the tri-plumbic arsenate. This may be due to the fact that the 
former has a larger per cent of arsenic and therefore a smaller quan- 
tity of it would give the same effect. It is probable, however, that 
the lead would possess some poisonous properties in this compound, 
and therefore the larger amount of lead in the one may somewhat 
offset the excess of arsenic in the other. Some' have claimed that 
the lead hydrogen arsenate was more injurious to foliage than the tri- 
plumbic arsenate, but this was not found to be the case during the 
three years of the experiments here reported. Taking all of these 

a Agriculture of Massachusetts, 1897, p. 386. 



HOME-MADE LEAD ARSENATE. 23 

facts into consideration, it would appear from our knowledge at the 
present time that the product prepared from lead nitrate is slightly 
more desirable. 

PHYSICAL PROPERTIES OF LEAD ARSENATE. 

The physical properties or characteristics of all insecticides wdiich 
are to be applied as a spray are very important. P'reshly jjrecipitated 
lead arsenate is a white, very light, flocculent compound, and it is 
hard to conceive of an insecticide possessing more desirable physical 
properties. When sprayed on foliage it forms a thin film over the 
leaf, and after once having been dried thereon it is with difficulty 
washed off by ordinary rains, and therefore need not be applied so fre- 
quently as some other insecticides. This is quite an important con- 
sideration, particularly as the greatest expense connected with spray- 
ing is the cost of applying the mixture. 

Another important point is the ease with which it may be kept in 
suspension in water. Such materials as Paris green, Scheele's green, 
and others which have a high specific gravity are with difficulty kept 
in suspension during spraying, and there is always great danger from 
the material becoming too concentrated in the bottom of the spray 
tank, thus causing too strong an application and resulting in the 
scorching of the foliage. Paris green is particularly objectionable in 
this regard, as it settles very rapidly unless thoroughly and constantly 
agitated. Lead arsenate shows considerable variation in the time of 
settling, depending upon the way in which it has been treated and also 
the chemicals from wdiich it has been made. If it has once been dried, 
on mixing w^ith w^ater again it settles out much more readily than if it 
has never been dried. It is for this reason that is is generally put on 
the market in the form of a paste. There is also a difference between 
that prepared from lead nitrate and that prepared from lead acetate. 
The former is more bulky and remains in suspension much longer. 
After drying there is very little difference in rapidity of settling 
between the products made from the different lead salts. Plate I 
shows graphically the variation in settling observed among prepara- 
tions of lead arsenate which have received different treatments. As 
stated in the legend, tube a is lead arsenate prepared from sodium 
arsenate and lead acetate; in tube h lead nitrate was used instead of 
the acetate ; tubes c and d are the same as tubes a and h, respectively, 
except that they have been dried out and then mixed with w^ater 
again. All of the samples represent the same amount of actual lead 
arsenate and the column of w^ater in each case is 12 inches high. All 
were thoroughly shaken and then photographed, fig. 1 after they had 
stood two minutes, and fig. 2 after they had stood fifty minutes. It 
will be noticed that after two minutes tube 6 had settled but very 
little, tube a about one-third of the way down, tube c nearly to the 



24 LEAD ARSENATE. 

bottom, and tube d about halfway down. Some of the finer particles 
still remain in suspension in tubes c and d, and the distinguishing line 
between the water and the main body of the precipitate is indistinct. 
After fifty minutes tube h is scarcely more than halfway down 
while the others have practically all settled to the bottom. 

III. ACTION OF LEAD ARSENATE ON FOLIAGE. 

GENERAL DISCUSSION. 

The fact is well known to entomologists, fruit growers, and others 
that the foHage of the stone fruits is very susceptible to injury by' 
many substances used as insecticides and fungicides, notably arseni- 
cals and Bordeaux mixture, when applied as a spray in sufficient 
strength to destroy insects and fungi. This is particularly true in 
regard to the peach, which seems to be the most delicate and easily 
injured of them all. For this reason entomologists have been en- 
deavoring for many years to find an insecticide that would destroy 
leaf-eating insects and not injure the most delicate foliage. The list 
of substances which may be used is somewhat limited, because of the 
fact that whatever the material may be it must be comparatively 
cheap and in such a physical condition as to be easily and thoroughly 
applied. There is no effective insecticide of this class known at the 
present time which can be used on the peach without more or less 
risk of injury. As a result of this condition, many peach growers 
have given up the use of arsenicals, and, in fact, in some sections many 
orchards have been abandoned entirely. This is a serious problem, 
and if a successful method can be discovered of combating these de- 
structive insects without injuring the tree or fruit it will mean millions 
of dollars to the peach industry. When lead arsenate was first used 
it was thought that it possessed all of the necessary qualifications and 
would prove to be the ideal insecticide. It is of inestimable value 
and is extensively used on apple and other more hardy foliage, and 
even on the peach it is often used without injury, as shown by many 
reports on the subject and as personally, observed by the authors. 
Some of the statements in regard to this point which have appeared 
in several experiment station bulletins and other reports on the sub- 
ject are quoted as follows: Fernald states that "it [arsenate of lead] 
can be used in large proportions, if necessary, even up to 25 pounds 
to 1 50 gallons of water, without injury to the foliage. "'=' "It does not 
injure the foliage of the most delicate plants, even when used in as 
large a proportion as 25 pounds, or even more, to 150 gallons of 
water." ^ Marlatt: "It may be used at any strength from 3 to 15 

a Massachusetts Hatch Exper. Sta., 1894, Bui. 24, p. 7. 
fc Agriculture of Massachusetts, 1897, p. 355. 



jl. 131, Burtaj of Chemistry, U. S. Dept. of Agricultur. 



Plate I. 




Fig. 1.— After Standing Two Minutes. 




Fig. 2.— After Standing Fifty Minutes. 

EFFECT OF DIFFERENT TREATMENTS ON THE SETTLING OF LEAD 

ARSENATE. 

a, Lead iiuetate u.sed; b, lead nitrate used; c and d, same a.s a and 6, but have been dried out 
and again mixed witli water. 



ACTION OF LEAD ARSENATE ON FOLIAGE. 25 

pounds to the 100 gallons of water without injury to foliage. "'^ "It 
is totally without action on plants at any strength whatever, even 
when applied as a sirup." ^ Perkins:'^ "It does no injury to the 
foliage." Smith: "This combination has the advantage of being 
harmless to foliage, whatever the strength in which it is applied 

* * * . Its great advantage is its harmlessness to plant life of 
all kinds. "'^ "It is absolutely harmless to foliage at any strength 

* * * . It is the only effective poison of this character that 
can be safely ap])lied to peach foliage and on conifers."^ Stene:^ 
"It has the great advantage over most of our insecticides that it is 
entirely harmless to all plants in any strength." Bentley:^ "Ar- 
senate of lead will not burn foliage." Taft and Sliaw:'^ ';* * * 
it can be used upon the most tender foliage without injuring it, even 
though no lime is added." Green, Selby, and Gossard:* ''* * * 
if properly made from good materials, will burn foliage but little, no 
matter what strength is used." 

Others who have used and experimented with it have found that 
it frequently caused serious injury. In some of the cases reported 
peach trees to which it was applied were practically entirely defoliated. 
There are a number of causes to which this variation in the observa- 
tions of different investigators may be attributed. In the first place 
some of them are not based on experiments carried on for a sufficient 
length of time, or they have been conducted on apple or equally 
hardy foliage and the assumption made that the results would be 
the same on all foliage. No doubt, also, arsenate of lead of poor 
quality and containing an unnecessarily large amount of arsenic in 
a water-soluble form has been used in some cases, which woukl result 
in burning. In view of the analyses reported in Table I, page 9, 
it would appear that tliis might easily occur. Making allowance for 
all of these conditions, however, it is still evident that injury results 
at times from the use of properly made lead arsenate, while the same 
experiments carried out in the same way at a different time or place 
may not result in any injury. It is well known that the effect of 
insecticides and fimgicides in general on plants shows great variation 
in different parts of the United States, and even in the same place 
in different years, depending upon the temperature, moisture, and 
undetermined influences. Formulas that may be injurious to foli- 

alJ. S. Dept. Agr., 1898, Farmers' Bui. No. 19, p. 6. 
^Proc. Seventh Ann. Meeting, Assn. Econ. Ent., 1897, p. 24. 
c Seventh Ann. Rep., Vermont Agr. Exper. Sta., 1893, p. 124. 
<* Economic Entomology, 1896, p. 437. 
« New Jersey Agr. Exper. Sta., 1903, Bui. 169, p. 8. 
/Rhode Island Agr. Exper. Sta., 1904, Bui. 100, p. 138. 
P Tennessee Agr. Exper. Sta. Bui., 1905, vol. 18, No. 4, p. 36. 
'« Michigan Board of Agriculture, 1908, p. 397. 
i Ohio Agr. Exper. Sta., 1908, Bui. 199, p. 94. 
23904— Bull. 131—10 4 



26 



LEAD ARSENATE. 



age in some States may be used with safety in others. The injury 
to foHage from arsenicals in arid regions is less than in non-arid 
regions. Atmospheric conditions following spraying have a great 
influence on the action of the spray mixture on the foliage. As to 
why these conditions cause such variations in results no satisfactory 
explanation has ever been given. It is well known to chemists that 
pure arsenate of lead is practically insoluble in pure water, and it 
seems impossible that it can cause injury as long as it remains so. 
It has never been proven that leaves can absorb insoluble substances, 
but investigators have shown conclusively that they do absorb salts 
in solution. It would appear, therefore, that the lead arsenate must 
be acted upon by some solvent, rendering more or less of the arsenic 
soluble, before burning of the foliage will result. It was for the pur- 
pose of determining this important point, if possible, that this inves- 
tigation was begun. In order that the experiments may be carried 
out under the varying conditions presented by different seasons, it 
is the intention to conduct them for a number of years in succession, 
and while it is considered that the results obtained from the experi- 
ments conducted and reported herein are extremely suggestive they 
are not given as conclusive, but on account of the importance of the 
subject are presented as showing the progress that has been made. 

PREPARATION OF THE LEAD ARSENATE USED. 

That there might be no doubt of the purity of the lead arsenate 
used, it was prepared in the laboratory from pure chemicals and 
thoroughly washed. The product was then dried in order that it 
might be more conveniently handled and accurately weighed. 

No. 1 was made by adding a solution of crystallized lead acetate to 
a solution of crystallized sodium arsenate until the lead salt was in 
slight excess. The precipitated lead arsenate was allowed to settle, 
the supernatant liquid decanted, then the material was washed by 
decantation with pure water, and finally filtered and washed till the 
greater portion of the soluble impurities were removed, after which 
it was dried and powdered. 

No. 2 was prepared in the same way, except that pure lead nitrate 
was used instead of lead acetate. On analysis the samples showed 
the following composition : 

Table Y. — Analysis of lead arsenates prepared in the laboratory. 



Number of sample. 


Moisture. 


Total lead 

oxid 

(PbO). 


Total ar- 
senic oxid 
(AS2O5). 


Water-sol- 
uble im- 
purities. 


Water-sol- 
uble lead 
oxid 
(PbO). 


Water-sol- 
uble arsen- 
ic oxid 
(AS2O,). 


1 


Per cent. 

0:10 

.09 


Per cent. 
67.44 
64.02 


Per cent. Per cent. 
29.76 1.07 
32.64 1.57 


Per cent. 

0.56 

.53 


Per cent. 
0.40 


2 


.49 











ACTION OF LEAD ARSENATE ON FOLIAGE. 27 

Sample No. 1 agrees closely in composition with a mixture, in 
about equal proportions, of tri-plumbic arsenate (Pb3(As04)2) and 
plumbic hydrogen arsenate (PbHAsOJ, while No. 2 corresponds very 
closely to the theoretical composition of plumbic hydrogen arsenate. 

EXPERIMENTAL WORK OF 1907. 

The experiments were carried out on trees in the Bureau of Ento- 
mology orchard on the Department farm at Arlington, Va. Two 
types of fruit trees were selected, namely, apple, which is one of the least 
susceptible to injury from arsenicals, and peach, which is the most 
tender and easily injured of all fruit foliage. The only apple trees 
available for the experiments were young trees about 6 feet high, 
which had not reached the bearing age. The peach trees were large 
and had borne several crops of fruit. In applying the mixtures an 
ordinary barrel-sprayer outfit, fitted with a "Vermorel" double noz- 
zle, was employed. For each experiment there were used six apple 
and six peach trees. These were divided into two sections: A (three 
trees) received two applications and B (three trees) received three 
applications. 

DESCRIPTION OF EXPERIMENTS. 

Experiment 1. — To test the effect of pure lead arsenate made from sodium arsenate 
and lead acetate. Applied the material at the rate of IJ pounds of dry lead arsenate 
to 50 gallons of water. This is equivalent to about 2 pounds of a good grade of com- 
mercial lead arsenate to 50 gallons of water. 

Experiment 2. — Same as Experiment 1, except that freshly slaked quicklime was 
added at the rate of 4 pounds to 50 gallons of the spray mixture. (To determine to 
what extent the presence of lime would lessen or prevent burning of the foliage.) 

Experiment 3. — Same as Experiment 1, except that lead nitrate instead of the 
acetate was used in the preparation of the lead arsenate. (To show whether lead 
arsenate made from lead nitrate has a different action from lead arsenate made from 
lead acetate.) 

Experiment 4- — Same as Experiment 3, except that quicklime was added at the rate 
of 4 pounds to 50 gallons. 

Experiment 5. — To determine whether sodium acetate and acetic acid, which are 
formed as by-products when lead acetate acts on sodium arsenate, will scorch foliage. 
Applied a mixture of sodium acetate and acetic acid in the proportion of 9.6 ounces 
of crystallized sodium, acetate and 2.9 ounces of anhydrous acetic acid to 50 gallons of 
water. (These are the respective amounts of sodium acetate and acetic acid obtained 
in the making of 1^ pounds of dry lead arsenate, assuming that tri-plumbic arsenate 
is formed.) 

Experiment 6. — To determine whether the amount of sodium acetate used in Experi- 
ment 5, when used alone, will injure foliage. (Applied wash in the proportion of 9.6 
ounces to 50 gallons.) 

Experiment 7. — To determine whether sodium nitrate, which is formed as a by- 
product when lead arsenate is made from sodium arsenate and lead nitrate, will injure 
foliage. This was applied in the proportion of 10.4 ounces to 50 gallons of water, the 
theoretical amount of sodium nitrate formed in making IJ pounds of dry lead 
arsenate, using lead nitrate and assuming that plumbic hydrogen arsenate is formed. 



28 LEAD ARSENATE. 

Experiment 8. — To observe the effect of lead acetate on foliage to determine whether, 
if lead acetate were added in considerable excess, it would cause burning. Applied 
in the proportion of 2.7 ounces to 50 gallons of water. (This is 10 per cent of the theo- 
retical amount of lead acetate required to make 1^ pounds of dry lead arsenate.) 

Experiment 9. — To determine whether a still larger excess of lead acetate would 
burn when applied in the proportion of 5.4 ounces to 50 gallons of water. (This is 
20 per cent of the amount required to make 1^ pounds of dry lead arsenate.) 

Experiment 10. — To prove whether a small excess of lead nitrate would cause burning 
when applied in the proportion of 2.1 ounces to 50 gallons. (This is 10 per cent of the 
theoretical amount of lead nitrate required to make 1^ pounds of dry lead arsenate.) 

Experiment 11. — Same as Experiment 10, except that the material was applied at 
the rate of 4.2 ounces to 50 gallons, which is 20 per cent of the theoretical amount of 
lead nitrate required to make IJ pounds of dry lead arsenate. 

A number of trees were left unsprayed in different portions of the 
orchard for comparison. The spraying was done on the following 
dates: April 18, first apphcation on peach A and B, Experiments 1 to 
7, inclusive. The following day it rained, and on April 20 the appli- 
cation was made according to Experiments 8 to 11, inclusive. The 
foliage on the apple trees had not developed sufficiently at this date 
to be sprayed. The second application was made on peach A and B 
and the first application on apple A and B on April 29 and 30. April 

29 applied the spray in Experiments 1 to 9, inclusive, and on April 30 
in Experiments 10 and 11. On May 13 and 14 the third application 
was made on peach B and the second application on apple A and B. 
On May 13 applied spray in Experiments 1 to 4, inclusive, and 
finished on the following day. The third application on apple B was 
made on June 4. 

RECORD OF OBSERVATIONS. 

Observations were made on the condition of the foliage at intervals 
of one to two weeks, and a detailed record kept which it is not neces- 
sary to record here in full. It may be stated in the first place in 
regard to the apple that no noticeable injury whatever was caused to 
the foliage from any of the various mixtures, either in the case of 
two or three applications. The following notes apply only to the 
peach: 

June 4. On this date the last spraying was done and no evidence of any injury to 
the foliage was apparent which could be attributed to the materials previously ap- 
plied. A number of leaves showed split and ragged edges, but this was no doubt 
caused by a severe hailstorm which occurred on May 19. No scorching or burning 
of the foliage was noticeable. 

June 28. The foliage showed no injury except that on the trees in Experiment 11 B, 
which had been sprayed three times with the stronger solution of lead nitrate. This 
showed some spotting and the "shot hole" effect, though the injury was not serious. 
The amount of fruit on these trees was small, many of them did not have any at all, 
and, owing to the unfavorable weather conditions which had prevailed during the 
growing season, the fruit was all of inferior quality; however, that on the unsprayed 
trees was in a worse condition than on those to which lead arsenate had been applied. 

July 19. As far as the foliage was concerned, very little injury was apparent which 
could be attributed to the spraying mixtures. Experiment 3B showed slight leaf in- 



ACTION OF LEAD AKSENATE ON FOLIAGE. 



29 



jury, some of the leaves showing the "shot hole" effect, but not more than 2 or 3 per 
cent were so injured. As before noted, the small amount of fruit present was, as a rule, 
inferior, but this condition appeared to be due mainly lo fungus diseases. No fungi- 
cide had been applied, and the season was favorable to Ihe growth of fungi. 

August 7. No further injury was shown than that recorded in the i)receding obser- 
vations. A few peaches from trees sprayed with lead arsenate from either source 
had the appearance which arsenic injury frequently gives; that is, a dark, shriveled 
spot on the end, evidently where a drop of the spray had collected and concentrated. 
The greatest injury and in fact the only positive injury to foliage was shown in Ex- 
periments llA and llB, to which lead nitrate had been applied. 

August ^7. The fruit was just ripening at this date, but the crop was too small to 
draw any positive conclusions except in a general way. There was more fruit on 
the trees that had been sprayed with lead arsenate, and it was also in better condi- 
tion. That on trees s{)rayed with lead acetate and lead nitrate was in very good 
condition, but the amount was small. The main difference in the appearance of the 
fruit that had received the applications of lead arsenate, aside from the few cases 
noted, was its deep red color, which gave it a better appearance and, in this instance, 
in no way injured the quality. 

WEATHER CONDITIONS. 

Table VI shows the meteorological conditions for the period from 
March 1 to September 1, 1907, and Table VII gives a comparison 
between the temperature and rainfall for this season and the average 
data for tliirty-seven years. 

Table VI. — Monthly meteorological data, March to August, 1907, Washington, D. C. 

MARCH. 



Date. 


Temperature. 


Precipi- 
tation. 


Character of day. 


Possible 
sunshine. 


Maxi- 
mum. 


Mini- 
mum. 


Mean. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10.... 
11.... 
12.... 
13.... 
14.... 
15.... 
16.... 
17.... 
18.... 
19.... 
20.... 
21.... 
22.... 
23.... 
24.... 
25.... 
26. . . . 
27.... 
28. . . . 
29. . . . 
30.... 
31.... 

Mean 
or to- 
tal. 


"F. 
40 
61 
50 
44 
45 
40 
28 
48 
51 
35 
44 
44 
71 
73 
55 
62 
70 
61 
54 
58 
55 
90 
93 
85 
5() 
66 
80 
83 
92 
74 
56 


"F. 

31 
35 
28 
26 
30 
28 
22 
28 
33 
29 
27 
20 
43 
40 
36 
31 
38 
44 
40 
42 
32 
40 
50 
48 
39 
37 
46 
54 
55 
56 
41 


°F. 
36 

48 

■ 39 

35 

38 
34 
25 
38 
42 
32 
36 
35 
57 
56 
46 
46 
54 
52 
47 
50 
44 
65 
74 
66 
48 
52 
63 
68 
74 
65 
48 


Inches. 

0.26 

.19 

Trace. 

Trace. 
.02 
.00 
.02 
.08 

Trace. 
.'.'0 

Trace. 
.17 
.03 
.08 
.01 
.00 
.00 

Trace. 
.81 
.01 
.00 
.00 
.00 
,00 
.00 
.00 
.00 
.00 
.00 
.00 
.21 


Cloudy 


Per cent. 


65 
38 
90 
36 
91 

3 
40 
74 


83 



8 

6 
89 
96 
77 
75 


100 
45 
75 
84 
89 
75 
41 
70 
60 
98 
81 




Partly cloudy 


do " 


Clear 


Partly cloud v 


Clear " 


Cloudy 


Partly cloudy 


do 


Cloudy 


Clear 


Cloudy 


do 


do.. .. 


Clear 


do 


do 


Partly cloudy 


Cloudy ....." 


Clear 


Partly cloudy 


do 


do 

Clear 


do 


Cloudy. . . 


do 


Partly cloudy 

Clear. " 


do 


Cloudy 




60.] 


37.5 


48.8 


2.79 



30 



LEAD ARSENATE. 



Table VI. — Monthly meteorological data, March to August, 1907, Washington, D. C- 

Continued. 

APRIL. 



Date. 



10.. 
11.. 
12.. 
13.. 
14.. 
15.. 
16.. 
17.. 
18.. 
19.. 
20.. 
21.. 
22.. 
23.. 
24.. 
25.. 
26.. 
27.. 
28.. 
29.. 
30.. 

Mean 
or to- 
tal. 



Temperature. 



Maxi- 
mum. 



'F. 
45 
48 
65 
72 
74 
45 
40 
59 
49 
47 
53 
46 
49 
44 
51 
65 
48 
57 
48 
54 
58 
65 
61 
65 
79 
83 
61 
59 
71 
7S 



58.0 



Mini- 
mum. 



Mean. 



'F. 
37 
36 
47 
54 
60 
38 
36 
49 
42 
42 
44 
42 
44 
40 
42 
51 
43 
46 
43 
44 
46 
50 
56 
56 
60 
70 
54 
54 
62 
66 



48.4 



Precipi- 
tation. 



Inches. 

Trace. 

0.00 

.00 

Trace. 

Trace. 

.12 

.34 

.07 

1.06 

Trace. 
.00 
.01 
.00 
.00 
.00 
.00 
.00 
.00 
.21 
.00 
.00 
.00 
1.23 

Trace. 
.00 
.49 
.08 
.00 

Trace. 
.00 



3.61 



Character of day. 



Possible 
sunshine, 



Partly cloudy. 

Clear 

do 

Partly cloudy. 

do 

Cloudy 

do 

Partly cloudy. 

do 

do 

do 

Cloudy 

do 

Partly cloudy. 

Clear 

Partly cloudy. 

do ".. 

do 

Cloudy 

Partly cloudy. 

Clear 

Partly cloudy. 

Cloudy 

Clear 

do 

do 

Partly cloudy. 

Cloudy 

Partly cloudy. 
Cloudy 



Per cent. 

100 

100 

88 

57 

3 



41 

34 

62 

79 

33 

33 

47 

100 

54 

83 



66 

100 

71 

4 

100 

92 

75 

69 

22 

55 

53 



MAY. 



10.. 
11.. 
12.. 
13.. 
14.. 
15.. 
16.. 
17.. 
18.. 
19.. 
20.. 
21.. 
22.. 
23.. 
24.. 
25.. 
26.. 
27.. 
28.. 
29.. 
30.. 
31.. 



Mean 
or to- 
tal. 



f)S 


51 


60 


60 


48 


54 


65 


49 


57 


70 


46 


58 


62 


39 


50 


71 


51 


61 


62 


57 


60 


71 


52 


62 


67 


54 


60 


78 


52 


65 


62 


42 


52 


59 


39 


49 


73 


44 


58 


85 


r,! 


68 


83 


59 


71 


70 


57 


64 


70 


54 


62 


83 


53 


68 


84 


62 


73 


67 


50 


58 


60 


41 


50 


70 


39 


54 


74 


56 


65 


66 


56 


61 


58 


46 


52 


61 


46 


54 


72 


51 


62 


64 


44 


54 


72 


42 


57 


74 


49 


62 


61 


52 


56 


69.1 


49.4 


59.2 



0.61 
.00 

Trace. 
.13 
.00 
.52 

Trace. 
.48 
.24 

Trace. 
.05 
.00 
.00 
.00 
.01 
.39 
.00 

Trace. 
1.10 
.10 
.00 
.00 
.01 
.23 
.14 
.20 
.58 
.00 
.00 
.00 
.24 



5.03 



Cloudy 

do 

Partly cloudy. 

Clear 

do 

Cloudy 

do 

Clear 

Cloudy 

Clear 

do 

do 

do 

do 

Partly cloudy. 

Cloudy 

Partly cloudy. 

Clear 

Partly cloudy. 

do 

Clear 

do 

Cloudy 

do 

do 

do 

Partly cloudy. 

Clear 

do 

do 

Cloudy 



49 

69 

100 

10 



70 

18 

85 

75 

100 

100 

100 

73 



51 

76 

51 

34 

100 

86 

20 

12 

4 



35 

87 

79 

100 





ACTION OF LEAD ARSENATE ON FOLIAGE. 



31 



Table VI. — Monthly incleorological data, March to August, 1907, Washington, D. C- 

Continued. 

JUNE. 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10.... 
11.... 
12.... 
13.... 
14.... 
15.... 
16.... 
17.... 
18.... 
19.... 
20. . . . 
21.... 
22.... 
23.... 
24.... 
25.... 
26.... 
27.... 
28.... 
29.... 
30.... 

Mean 
or to- 
tal. 



Temperature. 



Maxi- 
mum. 



°F. 



85 



75.1 



Mini- 
mum. 



Mean. 



Precipi- 
tation. 



Inches. 

2.20 

.14 

.00 

Trace. 
.16 
.00 
.11 
.21 
.00 

Trace. 
.81 
.05 
.09 
.07 
.00 
.00 
.00 
.00 

Trace. 
.00 
.00 
.00 
.00 

Trace. 
.01 
.06 
.00 
.01 
.94 
.00 



Character of day. 



Cloudy 

do 

Partly cloudy. 

Clear." 

Partly cloudy. 

Clear ". . 

do 

Cloudy 

Clear 

do 

Cloudy 

do 

do 

do 

Clear 

do 

do 

do 

Partly cloudy. 

do 

Clear 

do 

Partly cloudy. 

Clear." 

do 

do 

do 

Partly cloudy. 

Cloudy 

Partly cloudy. 



Possible 
sunshine 



Per cent. 


53 
65 
62 
80 
69 
20 
100 
69 

1 
3 

64 
100 
100 
66 
48 
40 
100 
78 
52 
65 
79 
69 
87 
64 
70 
32 



JULY. 



1.... 

2.... 

3.... 

4.... 

5.... 

6.... 

7.... 

8.... 

9.... 

10... 

11... 

12... 

13... 

14... 

15... 

16... 

17.... 

18.... 

19... 

20... 

21... 

22... 

23... 

24... 

25... 

26... 

27... 

28... 

29... 

30.... 

31.... 

Mean 
or to- 
tal. 


86 
85 
77 
81 
81 
86 
90 
93 
85 
91 
93 
82 
80 
84 
82 
88 
85 
91 
87 
90 
83 
87 
88 
91 
92 
86 
80 
83 
72 
86 
85 


59 
65 
58 
52 
57 
63 
66 
73 
72 
68 
70 
08 
03 
61 
64 
72 
73 
74 
72 
74 
66 
62 
71 
69 
71 
09 
61 
62 
65 
65 
63 


72 
75 
68 
66 
69 
74 
78 
83 
78 
80 
82 
75 
72 
72 
73 
80 
79 
82 
80 
82 
74 
74 
80 
80 
82 
78 
70 
72 
68 
76 
74 


0. 27 
.00 
.00 
.00 

Trace. 
.00 

Trace. 
.00 

Trace. 
.02 

Trace. 
.04 
.00 
.00 
.00 

Trace. 
.31 

Trace. 

Trace. 

Trace. 
.00 

Trace. 
.00 
.00 
.02 

Trace. 
.00 
.00 
.89 
.00 
.00 


Clear 


85 
74 
97 
84 
68 
84 
88 
67 
54 
57 
68 
18 
65 
83 
35 
61 
36 
36 
56 
57 

100 
80 
82 
83 
76 
43 
97 
55 

99 

100 




Clear 


do 


Partly cloudy 


Clear . 


do 


do 


Partly cloudy 


d"o " 


do 


Cloudy 


Partly cloudy 


do ." 


do.. .. 


Cloudy 


do 


.do. 


Partly cloudy 


do 


Clear . . . 


Partly cloudy 

Clear". " 

do 


Cloudy 

Clear 




Cloudy 


Clear 


do 




85.5 


66. 1 


75.8 


1.55 



32 



LEAD AESEKATE. 



Table W.— Monthly meteorological data, March to Augu.H, 1907, Washington. D.C. 

Continued. 



AUGUST. 



Date. 


Temperature. 


Precipi- 
tation. 


Character of day. 


Possible 

sunshine. 


Maxi- 
mum. 


Mini- 
mum. 


Mean. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10.... 
11.... 
12.... 
13.... 
14.... 
15.... 
16.... 
17.... 
18.... 
19.... 
20. . . . 
21.... 
22....' 
23.... 
24.... 
25.... 
26.... 
27.... 
28. . . . 
29.... 
30.... 
31.... 

Mean 
or to- 
tal. 


87 
89 
78 
78 
79 
88 
89 
91 
76 
76 
80 
88 
85 
77 
79 
76 
88 
80 
81 
82 
88 
73 
72 
86 
78 
81 
77 
80 
78 
80 
80 


°F. 

06 
67 
62 
58 
59 
67 
67 
67 
66 
66 
70 
67 
71 
62 
56 
66 
68 
65 
60 
70 
67 
58 
56 
67 
66 
55 
58 
63 
60 
57 
59 


°F. 
76 
78 
70 
68 
69 
78 
78 
79 
71 
71 
75 
78 
78 
70 
68 
71 
78 
72 
70 
76 
78 
66 
64 
76 
72 
68 
68 
72 
69 
08 
70 


Incites. 
0.00 
.00 
.79 
.01 
.12 
.43 
.00 
.00 
.67 
.40 
.00 
.00 
.09 
.00 
.00 

Trace. 

Trace. 
.04 
.00 
.70 
.20 

Trace. 
.64 
.25 
.00 
.00 

Trace. 
.00 
.00 

Trace. 
.00 


Partly cloudy 


Per cent. 
42 
84 
24 
100 
20 
59 
75 
81 



9 
36 
72 
61 
74 
100 

7 
57 

6 
99 
34 
55 
39 


79 
99 
98 
10 
34 
100 
21 
66 


Clear 


Cloudy 


Clear 


Cloudy 


Partly cloudy 


Clear " 


do 


Cloudy 


do 


do 


Clear 


Partly cloudy 


Clear ". . 


do 


Cloudy 


Partly cloudy 


Cloudy 


Clear 


Partly cloudy 


do ." 


do 


Cloudy 


Partly cloudy.. . 


Clear 


do 


Cloudy 


Partly cloudy. .. 


Clear 


Partly cloudy 


do 




81.3 


03.4 


72.4 


4.34 



Table VII.- 



-Comparifson of monthly meteorological data for 1907 with the average for 
thirty-seven years. 




SUMMARY FOR 1907 



Summing up tlie results for the season it can be stated that no 
injury resulted to the foliage of the apple from any of the mixtures 
applied, and only very slight injury to that of the peach, none of 



ACTION OF LEAD ARSENATE ON FOLIAGE. 33 

which was of a decided enough character to attribute it with cer- 
tainty to the spraying. Some of the trees which had not been 
sprayed at all showed a condition which would have been attributed 
to spraying injury if it had not been known that no insecticide had 
been applied to them. The most positive results were shown on 
trees which had received the applications of lead nitrate, but the 
fruit on these trees did not appear to have been injured in the least. 
By referring to the meteorological report for the period several 
striking facts will be noticed. March, the month preceding spray- 
ing, was unusually warm, the mean being 6.6° higher than the 
average of the month for the preceding thirty-seven years, and also 
higher than for the month following. This caused the trees to put 
out their foliage very early. Following this the temperature was 
below normal for the entire growing season to the following extent: 
April 4.5°, May 4.8°, June 7.1°, July 1.1°, and August 2.6° below 
the daily average for these months for the preceding thirty-seven 
years. The rainfall for April, May, and June — the months when 
spraying was actually done — was considerably above the average, 
and the number of clear days for this period, was only about one in 
three. In every case rain fell on the same day or within two days 
after spraying. These abnormal conditions render the drawing of 
any satisfactory conclusions from this year's work impossible. The 
recorded experience of users of Paris green, other arsenicals, and 
Bordeaux mixture shows that greater injury has occurred following 
wet weather. This may be true in general, but when spraying is 
followed soon thereafter by heavy rain the material may be washed 
off to such an extent that injury would not result from the small 
amount remaining. Frequent rains which are just sufficient to thor- 
oughly wet the foliage would naturally produce conditions favorable 
to the maximum injury. 

EXPERIMENTAL WORK OF 1908. 

DESCRIPTION OF EXPERIMENTS. 

The results obtained in 1907 indicated that it was not necessary to 
continue experiments wdth two applications; therefore in 1908 three 
applications were made in all except one instance, to which attention 
is called later. The experiments were conducted on the same apple 
trees as in the preceding year, but conditions made it necessary to 
select peach trees in another orchard. These were young vigorous 
trees and were in their second bearing year. As they were not large, 
a five-gallon knapsack sprayer outfit was selected for the work as 
being more convenient. 



34 LEAD ARSENATE. 

All of the experiments made in 1907 were repeated this year with 
the following in addition : 

Experiment 12. — ^To test the effect of applying lead arsenate made from lead acetate 
and sodium arsenate without removing any of the by-products formed; i. e., sodium 
acetate, acetic acid, and a slight excess of lead acetate. 

Experiment 13. — Same as Experiment 12, except that lime was added in the propor- 
tion of 4 pounds to 50 gallons. 

Experiment 14- — To test the effect of lead arsenate made from lead nitrate and 
sodium arsenate without removing the by-products formed; i. e., sodium nitrate and 
a slight excess of lead nitrate. 

Experivient 15. — Same as Experiment 14, except that lime was added at the rate of 
4 pounds to 50 gallons. 

In these four experiments the lead arsenate was applied in the same 
proportion as in other experiments in which it was used; that is, on 
the basis of IJ pounds of dry material to 50 gallons of water. 

Four apple and four peach trees were used for each experi- 
ment. The first application was made on April 27 and the second on 
May 8. On May 20 the third application was made on the apple 
trees and Experiments 1 to 4 on the peach, when work was inter- 
rupted by a very heavy rain (1.86 inches), followed by several days of 
unsettled weather. On the 25th the remaining mixtures were ap- 
plied, and Experiments 1 to 4 were resprayed. The latter, therefore, 
had received four applications of lead arsenate, but as the third had 
not had sufficient time to dry completely on the leaves before rain 
fell it was undoubtedly largely washed off. The last application was 
followed by five days of very hot, clear weather without rain. 

RECORD OF OBSERVATIONS. 

When the last spraying was done, on May 25, there was no injury 
apparent from any of the apphcations previously made. June 4 no 
injury could be observed to any of the apple trees. The foliage of 
the peach, however, showed very decided injury in some cases, as 
noted below. 

NOTES MADE ON JUNE 4. 

Experiment 1. — Quite a number of leaves had brown, shriveled edges and showed 
the "shot hole" effect, the injury, however, not being severe. Experiments 2, 3, and 
4 the same, accompanied in the latter case by slight dropping and yellowing of the 
leaves. 

Experiment r,. — Evidence of very slight injury; Nos. 6, 7, and 8, no injury. 

Experiment 9. — Slight injury, some "shot-hole" effect; no dropping of leaves. 

Experiment 10. — Same as No. 9. 

Experiment 11. — Same as Experiment 9, but more severe; some dropping of leaves. 

Experiment 12. — Showed some injury; leaves pretty badly spotted, and some had 
dropped. 

Experiment 13. — Same as Experiment 12, but not so severe. 



Bui. 131, Bureau of Chemistry, U. S. Dept. of Agriculture. 



Plate II. 




Fig. 1 .—Leaves from Trees in Experiment 3. (Natural vSize.) 




Fig. 2.— Leaves from Trees in Experiment 12. (Reduced.) 
PEACH LEAVES SHOWING INJURY FROM LEAD ARSENATE, 



ACTION OF LEAD ARSENATE ON FOLIAGE. 35 

Experiment 14. — A few leaves had fallen, but the injury was less marked than in 
Experiment 12. 
Experiment 15. — Practically the same as Experiment 14. 

Plate II, fig. 1, shows the appearance of leaves on June 4, injured 
by lead arsenate. These were selected from trees in Experiment 3 
as representative. Figure 2 shows some of the most severely injured 
leaves taken irom Experiment 12. 

NOTES MADE ON JUNE 9. 

Apple trees showed no injury. The notes on the peach trees were 
as follows: 

Experiment 1. — Considerable injury to foliage; a great maaiy leaves had fallen, as 
evidenced by the thin appearance of the foliage and the number of leaves on the 
ground. 

Experiment 2. — Injury very evident, but not so severe as in Experiment 1. A few 
leaves had fallen. 

Experiment 3. — Many leaves with "shot holes," but as a whole the injury appeared 
to be slightly less than in Experiment 1. 

Experiment 4- — Practically the same as Experiment 2, except that a few more leaves 
had fallen. 

Experiment 5. — A little "shot holing" of leaves, but none had fallen. As a whole 
the trees looked healthy and in good condition. 

Experiment 6. — No injury noticeable. 

Experiment 7. — Foliage in good condition; fine green color; no injury. 

Experiment 8. — No injury. 

Experiment 9. — Injury slight; a few "shot holes;" no fallen leaves. 

Experiment 10. — Same as Experiment 9. 

Experiment 11. — Some injury; many leaves with numerous "shot holes," but few 
had fallen. 

Experiment 12. — Quite severely injured. Many fallen leaves and foliage noticeably 
thin on tree. Many leaves were yellow and had numerous "shot holes." 

Experiment 13. — Considerable injury, but not so severe as in Experiment 12. Not 
many yellow leaves. 

Experiment 14- — Practically the same as Experiment 12. 

Experiment 15. — Same as Experiment 13. 

NOTES MADE ON JULY 29 ON CONDITION OF FRUIT. 

Apple foliage uninjured; no fruit. Notes on the peach trees were 
as follows: 

Experiment 1 . — Fruit nearing maturity, very much redder in color than that on trees 
not sprayed with arsenicals. Many peaches, approximately 40 per cent, showed the 
injurious effect of spraying by having a brown or black shriveled spot usually around 
or near the stem end or on the upper side. In some cases the injury showed on the 
small end, when the fruit was hanging down, presumably a drop of the liquid having 
collected there and concentrated. 

Experiment 2. — Same as Experiment 1; injury not so severe. 



36 LEAD ARSENATE. 

Experiment 3. — Same as Experiment 1 ; no more severe. 

Experiment 4- — Same as Experiment 2. 

Experiment 5. — Fruit normal color (green); not injured from spraying. 

Experiments 6, 7, and 8. — Same as No. 5. 

Experiments 9, 10, and 11. — Fruit in good condition; normal color. 

Experiment 12. — Injury about the same as in Experiment 1 but not so severe; a 
smaller per cent of injured fruit, probably not over 30. 

Experiment 13. — Fruit deep red in color, as was all that sprayed with lead arsenate; 
not over 10 per cent showed injured spots and these were not so large nor deep as in 
Experiment 12. 

Experiment 14- — Injury i)ractically the same as in Experiment 12. 

Experiment 15. — Fruit not so red; injury about the same as Experiment 13. 

The presence of lime showed some beneficial effect by lessening the 
injury to the fruit as well as to the foliage. The fruit on unsprayed 
trees was still deep green in color and about one week behind that 
spraj^ed with lead arsenate as to maturity. All trees were in a healthy 
looking condition aside from the fact that Experiments 1 to 4 and 12 
to 15, inclusive, were not so thickly foliated, owing to previous drop- 
ping of the leaves. The fruit on these trees, in addition to being a 
deep red, was more fully matured, and ripened about a week earlier 
than that unsprayed. 

Plate III shows the trees on the unsprayed plot with normal 
healthy foliage. Plate IV represents a tree in Experiment 12 
sprayed with lead arsenate and showing partial defoliation, leaving 
the fruit largely exposed. Most of tlie leaves on the ends of the 
branches came out after the spraying was done, thus masking to a 
large extent the injury produced. 

NOTES MADE ON AUGUST 13 ON CONDITION OF FRUIT. 

These observations on the peach crop may be generalized. Experi- 
ments 1 to 4, inclusive, and 12 to 15, inclusive, in which lead arsenate 
had been applied, showed about 50 per cent of injured fruit when no 
lime was uSed and about 25 per cent injured when lime was applied. 
That showing the worst injury was somewhat shriveled and usually 
dropped before having fully matured. In other cases it showed a 
dark shriveled spot, usualh^ around the stem end, but frequently on 
the upper side or on the small end. This condition is brought out in 
fig. 1, which shows some of the most seriously injured fruit that 
remained on the trees. The per cent of insect injury, as shown by 
wormy fruit, was very small, in no case over 5 per cent of the total. 

Experiment 9, in which lead acetate was used, yielded more 
perfect fruit than any of the other trees sprayed; 90 per cent of it 
was sound, 80 per cent of which was of good size and practically 
perfect, while 10 per cent showed insect injury. 



Bui. 131, Bureau of Chemistry, U. S. Dept. of Agriculture. 



Plate III 




Bui. 131, Bureau of Chemistiy, U. S. Dept. of Agriculture. 



Plate IV. 




ACTION OF LEAD ARSENATE ON FOLIAGE. 



37 



The fruit from iill of the other sprayed trees was in practically the 
same condition as that from the unsprayed trees, none of tlie mix- 
tures having lessened insect injury except lead nitrate, which was 
effective to a slight extent. Fruit from the unsprayed trees was 
very much gummed; from 50 to GO per cent was wormy, and not over 
30 ])er cent was sound and marketahle. 




Fig. 1. — Injured peaches from trees sprayed with lead arsenate. (Reduced.) 
WEATHER CONDITIONS. 

The tables following give the meteorological conditions for the 
period from March 1 to September 1, 1908, and a comparison of the 
average data for thirty-eight years with those for the season of 1908. 



38 



LEAD ARSENATE. 



Table VIII. — Monthly meteorological data, March to August, 1908, Washington, D. C. 

MARCH. 



Date. 



Mean 
or to- 
tal .. 



Temperature. 



Maxi- 
mum. 



56. 



Mini- 
mum. 



Mean. 



°F. 
32 
44 
40 
36 
34 
36 
50 
44 
39 
40 
47 
55 
51 
56 
60 
52 
44 
46 
52 
34 
36 
44 
52 
56 
49 
58 
69 
68 
58 
46 
46 



Precipi- 
tation. 



Inches. 
0.20 
.02 
.00 
.00 
.10 
.59 
.00 
.00 
.27 
.00 
.00 

Trace. 
.00 

Trace. 
.04 

Trace. 

Trace. 

Trace. 
.21 
.00 
.00 

Trace. 
.32 
.00 
.00 
.00 
.00 
.05 
.35 
.00 
.30 



Character of day. 



Cloudy 

do. 

Partly cloudy. 

Clear 

Cloudv 

do 

Clear 

Partly cloudy. 

Cloudy 

Clear 

Partly cloudv. 

Clear ". . 

Partly cloudy. 
Clear ". . 



Cloudy 

Partly cloudy. 

do 

Cloudy 

Partly cloudy. 

Cloudy 

Clear 

Partly cloudy. 

Cloudy 

Partly cloudy. 

do 

Clear 

do 

Cloudv 

do 

do 

do 



APRIL. 



1 


51 


44 


48 


0.08 


2 


63 


38 


50 


.21 


3 


41 


32 


36 


Trace. 


4 


51 


33 


42 


.00 


5 


53 


20 


41 


.03 


6 


69 


48 


58 


.00 


7 


77 


44 


60 


.00 


8 


75 


58 


66 


.43 


9 


70 


43 


56 


.07 


10.... 


53 


40 


46 


.15 


11.... 


69 


46 


58 


.01 


12.... 


62 


41 


52 


.00 


13.... 


78 


40 


59 


.00 


14.... 


60 


40 


50 


.00 


15.... 


64 


47 


56 


.28 


16.... 


63 


38 


50 


.01 


17.... 


57 


35 


46 


.00 


IS.... 


60 


44- 


52 


.10 


19.... 


72 


51 


62 


Trace. 


20.... 


80 


44 


62 


.00 


21.... 


60 


43 


52 


.00 


22.... 


76 


39 


58 


.00 


23.... 


83 


55 


69 


.00 


24.... 


87 


54 


70 


.00 


25.... 


76 


57 


66 


.02 


26.... 


85 


58 


72 


.00 


27.... 


85 


65 


75 


.03 


28.... 


71 


56 


04 


.00 


29.... 


76 


46 


61 


.00 


30.... 

Mean 


68 


42 


55 


.17 










or to- 










tal.. 


67.8 


45.0 


50.5 


1.59 



Cloudj' 

Partly cloudy. 

do 

....do 

....do 

Clear 

do 

Cloudy 

Partly cloudy. 

Cloudy 

Partly cloudy. 

Clear 

do 

do 

Cloudy 

Clear 

do 

Cloudy 

Partly cloudy. 

Clear." 

do 

do 

do 

do 

Partly cloudy. 

Clear 

Partly cloudy. 

do 

Clear 

Partly cloudy. 



Possible 
sunshine. 



Per cent . 



4 
81 
85 

4 


100 
66 


100 
86 
100 
86 
100 
34 
72 

4 
10 
45 
11 
100 
75 


65 
68 
88 
90 

6 
18 
41 







74 
100 
91 
91 

82 
100 
4 
57 
100 
100 
100 
94 
92 
47 
100 
64 
65 
93 
44 



ACTION OP LEAD ARSENATE ON FOLIAGE. 



39 



Table Ylll. — Monthly meteorological data, March to August, 1908, Washington, D. C— 

Continued. 



MAY. 





Tei 


Date. 






Maxi- 




mum. 




'F. 


1 


56 


2 


66 


^ 


62 


4 


52 


5 


55 


6 


50 


7 


64 


8 


64 


9 


60 


10.... 


64 


11.... 


82 


12.... 


88 


13.... 


87 


14.... 


88 


15.... 


58 


16.... 


63 


17.... 


80 


18.... 


78 


19.... 


74 


20.... 


81 


21.... 


75 


22.... 


84 


23.... 


81 


24.... 


85 


25.... 


87 


26.... 


88 


27.... 


89 


28.... 


92 


29.... 


82 


30.... 


83 


31.... 
Mean 


85 




or to- 




tal . . 


74.3 



Temperature. 



Mini- 
mum. 



Mean. 



39 

44 

44 

42 

45 

46 i 

47 

51 

49 

44 

42 

63 

61 

58 

52 

51 

58 

60 

61 

61 

64 

64 

66 

63 

64 



Precipi- 
tation. 



Inches. 
0.00 
.04 
.00 
.29 
.32 
.35 
1.01 

Trace. 
.04 
.00 
.00 

Trace. 

Trace. 
.06 
.13 
.01 
.00 

Trace. 
1.20 
1.86 

Trace. 

Trace. 
.05 
.00 
.00 
.00 
.00 
.00 
.00 
.74 
.00 



Character of day. 



Clear 

Partly cloudy. 

do 

Cloudy 

do 

do 

do 

Partly cloudy. 

do 

Clear 

do... 

Partly cloudy. 

do 

do 

Cloudy 

Partly cloudy. 

do 

do 

Cloudy 

do. 

Partly cloudy. 

do 

do 

do 

Clear 

do 

do 

do 

Partly cloudy. 

do 

do 



JUNE. 



Possible 
sunshine, 



■ cent. 
92 





2 
42 
55 
100 
100 
52 
83 
55 

7 
56 
69 
12 
40 
24 
69 
54 
81 
82 
79 
87 
99 
60 
59 



1 

2 

3 

4 

5 

6 

7.... 

8 

9.... 

10... 

11... 

12.... 

13.... 

14... 

15.... 

16... 

17... 

18... 

19... 

20... 

21... 

22... 

23... 

24... 

25... 

26... 

27... 

28... 

29... 

30... 

Mean 
or to 
tal. 


72 
80 
74 
67 
78 
68 
81 
85 
87 
82 
73 
82 
84 
84 
78 
74 
75 
78 
88 
89 
89 
89 
94 
97 
85 
80 
83 
85 
92 
87 


59 
56 
58 
58 
57 
59 
52 
59 
64 
05 
61 
56 
58 
66 
58 
54 
52 
58 
60 
70 
70 
68 
68 
76 
71 
64 
57 
57 
67 
71 


66 
68 
66 
62 
68 
64 
66 
72 
76 
74 
67 
69 
71 
75 
68 
64 
64 
68 
74 
80 
80 
78 
81 
86 
78 
72 
70 
71 
80 
79 


0.00 
.00 
.09 
.46 
.00 
.00 
.00 
.00 
.02 

Trace. 
.02 
.00 
.00 
.00 
1.00 
.00 
.00 
.00 
.00 
.00 

Trace. 
.00 
.00 
.00 
.01 
.00 
.08 
.00 
.00 
.05 


Clear 


97 
99 
66 
9 
72 
7 
82 
99 
82 
74 
30 
99 

100 
99 
29 
99 

100 
70 
99 
60 
83 
91 
88 
88 
64 
85 
76 
93 
99 
72 


.do.. . 


Partly cloudy 


Cloudy 


Clear. . ... 


Cloudy 


Partly cloudy. 


Clear 


do 

Partly cloudy. 


do 


Clear. . 


do 


.. .do 




Clear. . 


Partly cloudy 


do 


Clear 


Partly cloudy 


do 


do 


Clear. . 


do 


Partly cloudy. 


do 


Clear. . 


do 


Partly cloudy 


Clear.. 




82.0 


61.6 


71.8 


1.73 



40 



LEAD ARSENATE. 



Table VIII. — Monthly meteorological data, March to August, 1908, Washington, D . C. 

Continued. 



JULY. 



9... 

10.. 

11.. 

12.. 
13.. 
14.. 
15.. 
16.. 
17.. 
18.. 
19.. 
20.. 
21.. 
22.. 
23.. 
24.. 
25.. 
26.. 
27.. 
28.. 
29.. 
30.. 
31.. 

Mean 
or to- 
tal 



Date. 


Temperature. 


Precipi- 
tation. 


Character of day. 


Possible 
Sunshine. 


Maxi- 
mum. 


Mini- 
mum. 


Mean. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10.... 

11.... 

12.... 

13.... 

14.... 

15.... 

16.... 

17.... 

18.... 

19.... 

20. . . . 

21.... 

22.... 

23.... 

24. . . . 

25.... 

26.... 

27.... 

28... 

29... 

30... 

31... 

Mean 
or to 
tal. 


°F. 
90 
90 
86 
88 
86 
94 
j 94 
i 81 
! 80 
1 79 
90 
99 
96 
1 96 
87 
81 
87 
91 
91 
90 
88 
87 
89 
88 
88 
81 
78 
84 
85 
84 
80 


°F. 
69 

72 
71 
73 
71 
72 
72 
64 
59 
60 
61 
68 
70 
74 
71 
62 
57 
72 
76 
71 
69 
70 
71 
69 
70 
71 
G8 
68 
66 
68 
72 


°F. 
80 
81 
78 
80 
78 
83 
83 
72 
70 
70 
76 
84 
83 
85 
79 
72 
72 
82 
84 
80 
78 
78 
80 
78 
79 
76 
73 
76 
76 
76 
76 


Incites. 

0.01 

.03 

Trace. 
.24 

Trace. 
.00 
.04 
.00 
.00 
.00 
.00 
.05 
.00 
.06 
.00 
.00 
.00 

Trace. 
.00 
.00 
.20 
.13 
.77 
.17 
.05 
.88 
.65 
.00 

Trace. 
.00 
.01 


Partly cloudy 


Per cent. 
86 
78 
58 
43 
56 
82 
98 
66 
67 
59 
92 
69 
93 
64 
78 
98 
78 
56 
71 
67 
57 
38 
41 
46 
38 
19 

3 
48 
62 
73 




do 


do 


.do 


. ..do 


do 


Clear 




do 


do 


Clear 


Partly cloudy. . 


Clear 


Partly cloudy. 


Clear 


do 


do 




..do 


.. ..do 


Cloudy 


..do 


do 


do 


do 


. .do 


do 




do 


do 


Cloudy 




87.4 


68.6 


78.0 


3.29 



AUGUST. 



84 


66 


75 


89 


59 


74 


92 


66 


79 


95 


70 


82 


89 


72 


80 


85 


71 


78 


87 


69 


78 


78 


65 


72 


70 


62 


66 


84 


60 


72 


86 


68 


77 


92 


65 


78 


93 


73 


83 


93 


72 


82 


88 


74 


81 


84 


68 


76 


87 


68 


78 


86 


70 


78 


89 


70 


80 


77 


59 


68 


80 


53 


66 


84 


69 


76 


79 


71 


75 


74 


66 


70 


68 


56 


62 


61 


57 


59 


63 


56 


60 


67 


58 


62 


76 


52 


64 


81 


52 


66 


81 


56 


68 


82.0 


64.3 


73.2 



0.00 
.00 
.00 
.00 
.02 
.06 
.01 

Trace. 
.86 
.00 
.00 
.00 
.00 
.00 
.00 

Trace. 

1.11 

.18 

.00 

Trace. 
.00 

Trace. 

Trace. 
.00 
1.84 
1.05 
.01 
.00 
.00 
.00 
.00 



Partly cloudy. 

Clear 

....do 

....do 

Cloudv 

....do 

....do 

....do 

....do 

Clear 

....do 

....do 

....do 

Partly cloudy. 

do 

Cloudy 

do 

Partly cloudy. 

Clear 

Partly cloudy. 

do 

Cloudy 

do 

do 

do 

do 

do 

do 

Clear 

do 

do 



65 

100 

89 

91 

36 

16 

26 

31 

1 

92 

85 

72 

99 

75 

57 

28 

18 

38 

68 

61 

74 

20 

15 

5 







6 

89 



ACTION OF LEAD ARSENATE ON FOLIAGE. 



41 



Table IX. — Comparison of monthly meteorological data for 1908 with the average 

for thirty -eight years. ♦ 



Month. 

March 

April 

May 

June 

July 

August 


Temperature. 


Rainfall. 


Mean 
for 
1908. 


Mean for 
thirtv- 
eight 
years. 


Average 

daily 
e.xcess or 
deficiency 

as com- 
pared with 
mean for 
thirty-eight 
years. 


Total 
for 
1908. 


Mean for 
thirty- 
eight 
years. 


Monthly 
excess or 
deficiency 

as com- 
pared with 
mean for 
thirty-eight 
years. 


47.4 
56.5 
65.2 
71.8 
78.0 
73.2 


"F. 
42.3 
53.0 
64.0 
72.6 
77.0 
74.6 


"F. 
+.5.1 
+3.5 
+1.2 
-0.8 
+ 1.0 
-1.4 


Inches. 
2.45 
1.59 
6.10 
1.73 
3.29 
5.14 


Inches. 
3.93 
3.14 
3.81 
4.08 
4.61 
4.43 


Inches. 
-1.48 
-1.55 
+2.29 
-2. 35 
-1.32 
+0.71 



SUMMARY FOR 1908. 

The results on the apple trees were the same as in 1907, that is, 
the foliage was not injured in any case from applications of pure lead 
arsenate or any of the by-products naturally formed in its manu- 
facture. 

Rather severe injury was caused to the foliage and fruit of the 
peach by pure lead arsenate, made either from lead acetate or lead 
nitrate, and the same was true when the salts formed as by-products 
in the making were not washed out, whether applied with or without 
lime. The fruit was of a deep red color wliich generally extended 
throughout the flesh, and maturity was hastened about one week. 

Lead nitrate caused severe injury to the foliage but not to the 
fruit. Lead acetate in the stronger application caused slight injury 
to the foliage, but very materially protected the fruit from insect 
injury. Sodium acetate and acetic acid, acetic acid alone, and 
sodium nitrate produced no injurious effect on the foliage or fruit 
in the strengths applied. 

The meteorological conditions from March to August, 1908, were 
very different from those for the same period in 1907. In general 
the temperature was considerably above the normal, and the rain- 
fall was very much below normal except for May and August. One-half 
of the total rainfall for May (nearly as much as the normal average 
for the month) fell on two consecutive days. During June and most 
of July the rainfall was very light. No injury from previous spray- 
ing could be detected on May 25, when the final apphcation was 
made. Five hot, clear days, without rain, followed this application, 
and on June 4, ten days after the application, very decided injury 
was observed. From the appearance of the fohage the injur}^ would 
probably have been noticeable several days previously, but no obser- 



42 LEAD ARSENATE. 

vations had been made. This would seem to indicate very strongly 
that practically all the injury resulted from this last application. 

SUMMARY OF RESULTS FOR THE TWO YEARS' EXPERIMENT. 

No injury resulted to apple foliage in either 1907 or 1908 from 
three apphcations of lead arsenate, made from sodium arsenate and 
lead acetate, or sodium arsenate and lead nitrate, when applied at 
the rate of IJ pounds (dry basis) to 50 gallons of water. 

No injury resulted to apple foliage in 1908 from the use of lead 
arsenate made by the two methods, from which the salts formed as 
by-products were not removed, when applied the same number of 
times and at the same rate. (This experiment was not tried in 1907.) 

No injury was caused to the foliage of the apple in 1907 or 1908 
by three applications of lead acetate or lead nitrate in strength 
greater than would occur in any but the most carelessly made lead 
arsenate. 

No injury was caused to the foliage of the apple in 1907 or 1908 
from three applications of sodium acetate and acetic acid, acetic acid 
alone, or sodium nitrate,** in strengths produced from the amounts 
formed in the preparation of IJ pounds of lead arsenate by the two 
methods, made to 50 gallons. These results were expected, as lead 
arsenate is being used in apple orchards very extensively in all parts 
of the country and with success. 

No noticeable injury resulted to peach fohage in 1907 from two 
or three applications of lead arsenate (made by the two methods) 
at the rate of IJ pounds (dry basis) to 50 gallons of water. The 
fruit from these trees was a bright red color, which was desirable 
rather than otherwise, as its quahty was not impaired. 

Three applications of lead arsenate of the same strength (made 
by the two methods) in 1908 caused very marked injury to peach 
foliage and also to the fruit. The same when applied with lime in 
the proportion of 4 pounds to 50 gallons produced considerable 
injury, but to a less extent. Injury to the fruit was decreased about 
50 per cent by the use of lime. 

In 1908 three applications of lead arsenate, made from sodium 
arsenate and lead acetate, and from sodium arsenate and lead nitrate, 
without removing the salts formed as by-products, resulted in the 
same injury as from the use of the washed product. The same 
applied with lime at the rate of 4 pounds to 50 gallons produced about 
50 per cent less injury to the fruit. 

Three applications of lead nitrate, in the proportion of 2.1 ounces 
and 4.2 ounces to 50 gallons of water, produced slight injury to peach 

a Lodeman reports injury to the foliage of apple and quince from the application 
of nitrate of soda at the rate of 2 ounces in 2 gallons of water. Cornell Agr. Exper. 
Sta., 1893, Bui. No. 60, p. 291. 



ACTION OF LEAD ARSENATE ON FOLIAGE. 43 

foliage in 1907 from the stronger application and very marked injury 
in 1908 from both strengths. No injurious effect on the fruit could 
be detected. 

Three applications of lead acetate at the rate of 2.7 ounces to 50 
gallons of water produced no injurious effect on fruit or foliage in 
either 1907 or 1908. Three applications of lead acetate at the rate 
of 5.4 ounces to 50 gallons produced no injurious effect in 1907 and 
slight injury to foliage in 1908. The use of the latter strength showed 
a very marked effect on the fruit in reducing the injury caused by 
insects. This material would probably prove very effective as an 
insecticide if applied frequently enough or if the applications were 
followed by a few days of dry weather. 

No injury was caused to the foliage or fruit of the peach in 1907 or 
1908 by three applications of sodium acetate and acetic acid, acetic 
acid alone, or sodium nitrate of the strengths in which they would 
occur in making 1 ^ pounds of lead arsenate without removing these 
products and making up to 50 gallons. 

As far as the protection of the fruit from insect injury is concerned, 
the lead arsenate was a success. 

GENERAL DISCUSSION OF PROBLEMS INVOLVED IN THE INVES- 
TIGATION. 

Naturally, the first question asked will be, Why did no injury 
result to the peach in 1907 from the application of lead arsenate, 
while in 1908, when the applications were made in the same way 
and of the same strength, serious injury resulted? Though our 
present knowledge is not sufficient to give a positive answer to this 
question, some very interesting results bearing on this point have 
been obtained. 

LEAD NITRATE VS. LEAD ACETATE. 

Contrary to the opinion held by many, lead arsenate made from 
sodium arsenate and lead nitrate did not cause any more injury than 
that made from sodium arsenate and lead acetate. Cases reported 
in which it has been more injurious may have been due to the pres- 
ence of lead nitrate in considerable excess, for lead nitrate, as these 
experiments have shown, is considerably more caustic in its effect 
on foliage than lead acetate. Lead arsenate prepared from lead 
nitrate possesses several qualities which make it slightly more 
desirable for spraying purposes than that prepared from lead acetate. 
These have been pointed out in Part II. It would be more dangerous 
to use, however, if not properly made — that is, if the lead nitrate were 
present in any considerable excess over that sufficient to combine 
with all the arsenic. The injury to the foliage caused by lead acetate 
appeared to be local in character, as it did not cause the leaves to fall 



44 LEAD ARSENATE. 

or turn yellow. In very minute quantities arsenic appears to exert 
a stimulating effect or act as a tonic, as it does on animals. It is 
probably this action which, by accelerating the functional activity 
of the leaf and producing more rapid assimilation, causes the excess- 
ive reddening and hastens the maturity of the fruit. On the other 
hand, if too large an amount is absorbed, it has a toxic effect, resulting 
in retarded assimilation, which in turn will cause the fruit to shrivel 
and drop before it has matured. 

SUSCEPTIBILITY OF PEACH FOLIAGE TO INJURY. 

It has not been satisfactorily explained why the stone fruits, the 
peach in particular, should be so susceptible to injury. Numerous 
investigators have carried on extensive experiments on this point 
with copper compounds, mostly Bordeaux mixture, and with Paris 
green, resulting in much valuable information on the subject and the 
advancement of several theories to account for it. Those who have 
given special study to the action of fungicides and insecticides on 
plants and foliage include numerous foreign investigators. Among 
those in this country the follomng may be mentioned: Gillette,'' 
Galloway,^ Galloway and Woods, '^ Fairchild,'^ Sturgis, « Bain,/ and 
Hedrick. o 

It has been shown that leaves formed in a moist atmosphere have 
a thinner and more easily permeable cuticle than those grown in a 
dry atmosphere, and that injury from Bordeaux mixture and arsen- 
icals is more severe in warm, damp weather. Gillette ^ says: "The 
oldest leaves are most susceptible to injury;" also, "foHage most 
exposed to dew and direct sunlight will be most injured by the 
arsenites, other things being equal. Leaves kept perfectly dry can 
hardly be injured by the arsenites." Woodworth and Colby:* "It 
has been demonstrated repeatedly that dry Paris green can be placed 
upon a leaf in any quantity and so long as the leaf remains dry no 
evil results will follow." 

No experiments have been made in this investigation with lead 
arsenate to determine whether or not injury would result to peach 
foliage in the absence of water. It was assumed that none would 
be caused, in view of the results obtained by others with Paris green, 

a Iowa Agr. Exper. Sta., 1890, Bui. 10. 

& U. S. Dept. Agr., Div. Veg. Path., 1892, Bui. 3; 1894, Bui. 7. 

c Proc. Soc.'Prom. Agr. Sci., 1895, p. 42. 

d U. S. Dept. Agr., Div. Veg. Path., 1894, Bui. 6. 

« Connecticut Agr. Exper. Sta., Ann. Rep., 1900, Pt. Ill, p. 219. 

/Tennessee Agr. Exper. Sta., 1895, Vol. 8, No. 3; 1902, Vol. 15, No. 2. 

g New York Agr. Exper Sta., 1907, Bui. 287. 

'ilowa Agr. Exper. Sta., 1890, Bui. 10, pp. 402-403. 

» California Agr. Exper. Sta., 1899, Bui. 126, pp. 10-11. 



ACTION OF LEAD ARSENATE ON FOLIAGE. 45 

which compound, under the usual conditions, is more injurious to 
fohage than lead arsenate. 

Duggar" reports an extreme case in which bright sunshine follow- 
ing rain caused the appearance of "shot holes" in peach foliage. 
Others have also reported injury under these conditions, and it has 
been attributed to the concentration of the sun's rays on one spot by 
means of the drops of water acting as a lens and causing burning. A 
disease of the peach, shown to be of bacterial origin, has also been 
reported,'' which produces "shot holes" in the foliage and which is 
much worse in wet seasons. 

The work here reported has shown that pure lead arsenate applied 
to tender foliage like the peach will, in some cases, cause serious 
injury, indicating, therefore, that there is some influencing condition 
not as yet satisfactorily determined which causes the material to be 
decomposed and the arsenic to go into solution. This fact led to 
other experiments in the effort to discover the cause of this decom- 
position. 

CAUSE OF THE DECOMPOSITION OF LEAD ARSENATE. 

EXPERIMENTS ON THE ACTION OF THE CARBON DIOXID OP THE AIR. 

The first idea that presented itself as a possible explanation for this 
decomposition of lead arsenate was that the carbon dioxid of the air 
might act on the lead arsenate, forming lead carbonate, and thus 
liberate the arsenic acid. This theory, however, did not seem to be 
very plausible from a chemical point of view and also owing to the 
lack of uniformity in the injury reported in different years and at 
different places, but it was decided to determine the point. In order 
to do so the following experiments were carried out : 

Experiment 1. — One gram of lend arsenate, made from sodium arsenate and lead 
acetate, was treated with 1,000 cc of cold distilled water which had been jireviously 
boiled to expel carbon dioxid. This was allowed to stand ten days, being shaken 
eight times each day, and was then filtered. At the end of ten days the amount of 
arsenic in the solution was determined. 

Experiment ,?.— One gram of lead arsenate made from sodium arsenate and lead 
nitrate was treated in the same way. 

Experiment 3. — Same as Experiment 1, except that unboiled distilled water was used 
and carbon-dioxid gas was run into the solution for about one-half hour each day for 
ten days. 

Experiment 4. — Same as Experiment 3, except that lead arsenate was used as in 
Experiment 2. 

Experiment 5. — Same as Experiment 3, except that the solution was kept at about 
50° C. during the day. 

Experiment 6.— Same as Experiment 4, heating to 50° C. each day. (This is 
probably a higher temperature than the material would ever attain on the tree.) 



"New York Cornell Agr. Exper. Sta., 1899, Bui. 164. 

t>Anu. Rep. Conn. Agr. Exper. Sta., 1903, p. 337; Mycologia, 1909, 1: 23. 



46 LEAD ARSENATE. 

Table X . — Results of experiments with carbon dioxid. 
[Arsenic in solution expressed as AS2O5.] 

Carbon-dioxid-free water: p„ cent. 

Experiment 1 0. 40 

Experiment 2 49 

Water with carbon dioxid added: 

Experiment 3 25 

Experiment 4 39 

Water with carbon dioxid added and warmed to 50° C: 

Experiment 5 33 

Experiment 6 43 

It will be seen from these experiments that lead arsenate is slightly 
less soluble in distilled water saturated with carbon dioxid, even when 
heated to 50° C, than in cold distilled water free from carbon dioxid. 
It would hardly be expected that the results could be otherwise on 
the tree. 

EXPERIMENTS ON THE SOLVENT ACTION OF WATER USED IN SPRAYING. 

It was then thought that possibly the water with which the lead 
arsenate was being mixed for spraying contained compounds that 
had a solvent action on the lead arsenate. To determine this and 
also at the same time to determine the action of dilute solutions of 
sodium chlorid and sodium carbonate (two salts occurring fre- 
quently in waters) on lead arsenate, the following experiments were 
made : 

Experiment 1. — One gram of lead arsenate, made from lead acetate, was treated 
with 1,000 cc of the water which was used in the spraying experiments, and allowed 
to stand at room temperature ten days, shaking it eight times each day. This was 
filtered and the amount of arsenic in the solution determined. 

Experiment 2. — Same as Experiment 1, except that lead nitrate was used in making 
the lead arsenate. 

Experiment 3. — Same as Experiment 1, except that the mixture was heated to about 
50° C. each day for ten days. 

Experiment 4. — Same as Experiment 2, except that the solution was heated as in 
Experiment 3. 

Experiment 5. — Same as Experiment 1, except that the lead arsenate was treated 
with 1,000 cc of distilled water, carbon-dioxid-free, in which had been dissolved 
2 grams of pure sodium chlorid. 

Experiment 6. — Same as Experiment 5, using lead arsenate prepared from lead 
nitrate. 

Experiment 7. — Same as Experiment 1, except that 1,000 cc of distilled water con- 
taining in solution 2 grams of pure sodium carbonate was used. 

Experiment 8. — Same as Experiment 7, using lead arsenate prepared from lead 
nitrate. 

The amount of arsenic in solution and the per cent based on the 
total arsenic present are given in the following table: 



ACTION OF LEAD AKSENATE ON FOLIAGE. 



47 



Table XI. — Results of experiments to determine solvent action of water constituents 

on lead arsenate. 

[Arsenic in solution expressed as AsjOs.] 





Arsenic in solution. 


Rind of lead arsenate and water treatment used. 


Per cent 
based on 
weight of 

lead 
arsenate 
taken. 


Per cent 
of total 
arsenic 

present. 


Water used in spraying experiments: 
Used cold— 


Per cent. 
5.24 
3.61 

8.42 

8.27 

9.20 
11.22 

9.56 
11.82 


Per cent. 
17.61 




11.06 


Heated to .50° C.— 


28.29 




25.34 


Water containing 0.2 per cent of sodium chlorid: 


30.91 




34.38 


Water containing 0.2 per cent of sodium carbonate: 


32.12 




36.21 







It will be seen from these results that a very large amount of 
arsenic has been dissolved, not only by the solutions of the two 
salts tried, but by the sample of water tested. It would appear, 
therefore, that the frequent injury reported from the use of lead 
arsenate may be due to the solvent action of the water used in apply- 
ing it. To elucidate this point the composition of the water that 
had been used in the spraying experiments reported herein was 
determined. The results are given in Table XII: 

Table XII. — Analysis of water used in spraying experiments. 
[Water Laboratory, Miscellaneous Division.] 



Constituent. 



Silica (SiOj) 

Sulphuric-acid radicle (SO4) 

Bicnrbonic-acid radicle (IICO3). . . 

Nitric-acid radicle { N O3) 

Chlorin (01) 

Iron and aluminum (Feand Al).. 
Calcium (Ca) 



Parts 


Grains 


per 


per 1 


million. 


gallon. 


23.2 


1.353 


7.4 


.432 


37.5 


2.187 


13.5 


.787 


20.5 


1.195 


.6 


.035 


5.5 


.321 



Constituent. 



Magnesium (Mg) 

Potassium (K) 

Sodium (Na) 

Oxygen (to form FejOa). 

Total 



Parts 

per 

million. 



4.3 

1.0 

20.9 



Grains 

per 
gallon. 



0.251 
.058 

1.219 
.012 



7.850 



HYPOTHETICAL COMBINATIONS 



Potassium chlorid (KCl) 

Sodium chlorid ( NaCl) 

Sodium nitrate ( NaNOa) 

Sodium sulphate (NajSOi) 

Magnesium sulphate (MgSO<) 

Magnesium bicarbonate (MgHCOs) 



1.9 


0.111 


32.3 


1.884 


18.5 


1.079 


9.9 


.577 


.9 


.052 


24.8 


1.446 



Calciiun bicarbonate (CaHCOg) . 

Ferric oxid ( FejOa) 

Silica (SiOj) 



Total. 



23. 



1.301 

.047 

1.353 



48 LEAD ARSENATE. 

While the total amount of dissolved salts occurring in this water 
is small, it will be noticed that the sodium chlorid content is rela- 
tively liigh, and to this the solvent action which this water exerts 
on lead arsenate is no doubt largely due. It would appear from 
these results that if certain salts commonly occurring in waters are 
present in more than very small amounts they will exert a solvent 
action on the lead arsenate. 

CONCLUSIONS. 

Referring again to the fact that no injury resulted in 1907 from 
the lead arsenate, while in 1908 severe damage followed the use of 
the same water and chemicals, this may be explained by the differ- 
ence between the two seasons with respect to climatic conditions. 
In 1907 every application was followed by cool, cloudy weather and 
rain within forty-eight hours. In 1908 the first two applications 
were followed by cool days and light rains soon thereafter, but the 
last application, which caused practically all of the injury, was 
followed by five clear, hot days and no rain. The dews at night 
would be sufficient to moisten the material, and when hot sunshine 
followed the conditions would be just right to dissolve the maximum 
amount of arsenic, and therefore cause the maximum injury. The 
salts (sodium chlorid and sodium carbonate and no doubt others 
which have not been tried), which cause the lead arsenate to be 
broken up, are readily soluble in water, and if their application were 
followed by rain they would be washed out, and therefore no injury 
should result. 

Headden," in a publication which has recently been issued, calls 
attention to the danger that may result from using water containing 
certain salts. He says : " It has often been asked at meetings of these 
orchardists whether it was a safe practice to use their surface alkali 
water in applying the lead arsenate and I have stated that it was 
not a good practice, for one could easily conceive of conditions under 
which the whole of the lead arsenate could be converted into sul- 
phate of lead and sodic arsenate be formed in solution. This state- 
ment never seemed to be an acceptable one. I have in this case 
not depended upon any chemical laws, however evident their ade- 
quacy might be, but took well-washed lead arsenate, a sample which 
we found by rigid test to be free from soluble arsenic, suspended 
1 gram of it in 2,000 times its weight of water and added 2 grams of 
Glauber's salt, allowed it to stand three days, filtered off a portion 
of it, concentrated by evaporation, and tested it for arsenic. I found 

o Colorado Agr. Exper. Sta., 1908, Bui. 131, p. 22. 



ACTION OF LEAD AESENATE ON FOLIAGE. 49 

that the arsenic had gone into sohition in very considerable quan- 
tities. A parallel experiment was carried out with salt, in which 
only 1 gram of salt was used to the 2,000 grams of water. This was 
not allowed to stand quite three days when 1,500 grams were filtered 
off, concentrated and tested for arsenic. This concentrated solu- 
tion was found to be so heavily charged with arsenic that only a 
small part of it gave an unmanageable amount of arsenic when 
brought into an active Marsh apparatus." 

Still more exhaustive experiments than those here reported are 
being made in the orchard this year, which it is hoped will definitely 
settle this point. It was deemed best to report the progress that has 
been made before waiting for the final conclusions or for the results 
of other experiments along the same line, some of which have sug- 
gested themselves since this work was begun. The full data obtained 
from the 1909 experiments have not as yet been collated, but some 
interesting results have been obtained and may be briefly mentioned. 
Lead arsenate was applied to peach trees in the same proportions 
as in previous experiments — that is, I3 pounds (dry basis) to 50 
gallons — and three applications were made. 

(1) When applied with spring water (analysis of which has been 
given), some injury to foilage resulted, but it was not nearly so 
marked as in the preceding year, and a longer time elapsed before 
the injury was noticeable. 

(2) When appHed with distilled water very slight injury occurred, 
noticeably less than when the spring water was used. 

(3) When applied with distilled water to which 10 grains per gal- 
lon of sodium chlorid had been added, rather serious injury resulted. 
When distilled water containing 40 grains of sodium chlorid per gal- 
lon was used, the injury was very much increased, practically 50 per 
cent of the foliage being affected. 

(4) When, applied with distilled water containing 10 grains of 
sodium carbonate per gallon, injury was noticeable fourteen days 
after the first application, and seven days after the third application 
the trees were almost completely defohated. 

(5) Applied with distilled water containing 10 and 40 grains of 
sodium sulphate per gallon, some injury resulted, but this was not 
so marked as that produced in the presence of sodium chlorid. 

In similar experiments where lime was added at the rate of 4 
pounds to 50 gallons, injury to the fohage was almost entirely pre- 
vented. 






LIST OF TABLES. 

Page. 

Table I. Composition of commercial lead arsenates 9 

II. Composition of lead acetates 14 

III. Composition of lead nitrates 15 

IV. Composition of sodium arsenates 16 

V. Analysis of lead arsenates prepared in the lal)oratory 26 

VI. Monthly meteorological data, March to August, 1907, Washington, D.C. 29 
VII. Comparison of monthly meteorological data for 1907 with the aver- 
age for thirty-seven years 32 

VIII. Monthly meteorological data, March to August, 1908, Washington, D.C. 

IX. Comparison of monthly meteorological data for 1908 with the aver- 38 

age for thirty-eight years 41 

X. Results of experiments with carbon dioxid 46 

XI. Results of experiments to determine solvent action of water con- 
stituents on lead arsenate 47 

XII. Analysis of water used in spraying experiments 47 

50 

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